diff --git a/libgomp/Makefile.in b/libgomp/Makefile.in
index 3ef05e6a3cb..431bc87b629 100644
--- a/libgomp/Makefile.in
+++ b/libgomp/Makefile.in
@@ -368,7 +368,6 @@ CFLAGS = @CFLAGS@
 CPP = @CPP@
 CPPFLAGS = @CPPFLAGS@
 CPU_COUNT = @CPU_COUNT@
-CXX = @CXX@
 CYGPATH_W = @CYGPATH_W@
 DEFS = @DEFS@
 DEPDIR = @DEPDIR@
@@ -436,6 +435,7 @@ SED = @SED@
 SET_MAKE = @SET_MAKE@
 SHELL = @SHELL@
 STRIP = @STRIP@
+SYSROOT_CFLAGS_FOR_TARGET = @SYSROOT_CFLAGS_FOR_TARGET@
 VERSION = @VERSION@
 XCFLAGS = @XCFLAGS@
 XLDFLAGS = @XLDFLAGS@
diff --git a/libgomp/configure b/libgomp/configure
index a12b30f1b0f..498bc084a86 100755
--- a/libgomp/configure
+++ b/libgomp/configure
@@ -656,6 +656,7 @@ tmake_file
 XLDFLAGS
 XCFLAGS
 config_path
+SYSROOT_CFLAGS_FOR_TARGET
 FLOCK
 CPU_COUNT
 LIBGOMP_BUILD_VERSIONED_SHLIB_SUN_FALSE
@@ -679,7 +680,6 @@ libtool_VERSION
 ac_ct_FC
 FCFLAGS
 FC
-CXX
 MAINT
 MAINTAINER_MODE_FALSE
 MAINTAINER_MODE_TRUE
@@ -11808,22 +11808,11 @@ fi
 
 
 
-# We optionally test libgomp C++ support, and for that want to use the proper
-# C++ driver, 'g++' (or 'xg++' for build-tree testing).  Given that build of
-# target libstdc++-v3 depends on target libgomp (see '../Makefile.def'), we
-# cannot make build of target libgomp depend on target libstdc++-v3: circular
-# dependency.  We thus cannot instantiate 'AC_PROG_CXX' here: we'd get
-# '-funconfigured-libstdc++-v3' (see '../configure.ac').  Therefore, just
-# capture 'CXX', and we'll fix this up at 'make check' time (see
-# 'testsuite/lib/libgomp.exp:libgomp_init').
-
-
 # Create a spec file, so that compile/link tests don't fail
 test -f libgfortran.spec || touch libgfortran.spec
 FCFLAGS="$FCFLAGS -L."
 
-# We need 'gfortran' to compile parts of the library, and test libgomp Fortran
-# support.
+# We need gfortran to compile parts of the library
 # We can't use AC_PROG_FC because it expects a fully working gfortran.
 #AC_PROG_FC(gfortran)
 case `echo $GFORTRAN` in
@@ -16580,6 +16569,8 @@ fi
 
 fi
 
+
+
 # Get target configury.
 . ${srcdir}/configure.tgt
 CFLAGS="$save_CFLAGS $XCFLAGS"
diff --git a/libgomp/configure.ac b/libgomp/configure.ac
index 1aad83a79da..49f7fb0dc82 100644
--- a/libgomp/configure.ac
+++ b/libgomp/configure.ac
@@ -151,22 +151,11 @@ AC_SUBST(enable_static)
 
 AM_MAINTAINER_MODE
 
-# We optionally test libgomp C++ support, and for that want to use the proper
-# C++ driver, 'g++' (or 'xg++' for build-tree testing).  Given that build of
-# target libstdc++-v3 depends on target libgomp (see '../Makefile.def'), we
-# cannot make build of target libgomp depend on target libstdc++-v3: circular
-# dependency.  We thus cannot instantiate 'AC_PROG_CXX' here: we'd get
-# '-funconfigured-libstdc++-v3' (see '../configure.ac').  Therefore, just
-# capture 'CXX', and we'll fix this up at 'make check' time (see
-# 'testsuite/lib/libgomp.exp:libgomp_init').
-AC_SUBST(CXX)
-
 # Create a spec file, so that compile/link tests don't fail
 test -f libgfortran.spec || touch libgfortran.spec
 FCFLAGS="$FCFLAGS -L."
 
-# We need 'gfortran' to compile parts of the library, and test libgomp Fortran
-# support.
+# We need gfortran to compile parts of the library
 # We can't use AC_PROG_FC because it expects a fully working gfortran.
 #AC_PROG_FC(gfortran)
 case `echo $GFORTRAN` in
@@ -356,6 +345,8 @@ if test -z "$FLOCK"; then
   AC_CHECK_PROG(FLOCK, perl, $srcdir/testsuite/flock)
 fi
 
+AC_SUBST(SYSROOT_CFLAGS_FOR_TARGET)
+
 # Get target configury.
 . ${srcdir}/configure.tgt
 CFLAGS="$save_CFLAGS $XCFLAGS"
diff --git a/libgomp/testsuite/Makefile.in b/libgomp/testsuite/Makefile.in
index d743e464cdc..4155350cf80 100644
--- a/libgomp/testsuite/Makefile.in
+++ b/libgomp/testsuite/Makefile.in
@@ -147,7 +147,6 @@ CFLAGS = @CFLAGS@
 CPP = @CPP@
 CPPFLAGS = @CPPFLAGS@
 CPU_COUNT = @CPU_COUNT@
-CXX = @CXX@
 CYGPATH_W = @CYGPATH_W@
 DEFS = @DEFS@
 DEPDIR = @DEPDIR@
@@ -215,6 +214,7 @@ SED = @SED@
 SET_MAKE = @SET_MAKE@
 SHELL = @SHELL@
 STRIP = @STRIP@
+SYSROOT_CFLAGS_FOR_TARGET = @SYSROOT_CFLAGS_FOR_TARGET@
 VERSION = @VERSION@
 XCFLAGS = @XCFLAGS@
 XLDFLAGS = @XLDFLAGS@
diff --git a/libgomp/testsuite/lib/libgomp.exp b/libgomp/testsuite/lib/libgomp.exp
index a143b5d0def..cab926a798b 100644
--- a/libgomp/testsuite/lib/libgomp.exp
+++ b/libgomp/testsuite/lib/libgomp.exp
@@ -91,19 +91,6 @@ proc libgomp_init { args } {
       setenv LANG C.ASCII
     }
 
-    if { $blddir != "" } {
-	# Fix up '-funconfigured-libstdc++-v3' in 'GXX_UNDER_TEST' (see
-	# '../../configure.ac').
-	set flags_file "${blddir}/../libstdc++-v3/scripts/testsuite_flags"
-	if { [file exists $flags_file] } {
-	    set flags [exec sh $flags_file --build-includes]
-	    verbose -log "GXX_UNDER_TEST = $GXX_UNDER_TEST"
-	    set GXX_UNDER_TEST [string map [list \
-	      " -funconfigured-libstdc++-v3 " " $flags " \
-					   ] $GXX_UNDER_TEST]
-	    verbose -log "GXX_UNDER_TEST = $GXX_UNDER_TEST"
-	}
-    }
     if ![info exists GCC_UNDER_TEST] then {
 	if [info exists TOOL_EXECUTABLE] {
 	    set GCC_UNDER_TEST $TOOL_EXECUTABLE
@@ -185,6 +172,11 @@ proc libgomp_init { args } {
 
     set ALWAYS_CFLAGS ""
     if { $blddir != "" } {
+	# If '--with-build-sysroot=[...]' was specified, use it for build-tree
+	# testing.
+	global SYSROOT_CFLAGS_FOR_TARGET
+	lappend ALWAYS_CFLAGS "additional_flags=${SYSROOT_CFLAGS_FOR_TARGET}"
+
         lappend ALWAYS_CFLAGS "additional_flags=-B${blddir}/"
         # targets that use libgomp.a%s in their specs need a -B option
         # for uninstalled testing.
diff --git a/libgomp/testsuite/libgomp-site-extra.exp.in b/libgomp/testsuite/libgomp-site-extra.exp.in
index c824d85f7ed..8de14f48976 100644
--- a/libgomp/testsuite/libgomp-site-extra.exp.in
+++ b/libgomp/testsuite/libgomp-site-extra.exp.in
@@ -1,4 +1,2 @@
 set FLOCK {@FLOCK@}
-set GCC_UNDER_TEST {@CC@}
-set GXX_UNDER_TEST {@CXX@}
-set GFORTRAN_UNDER_TEST {@FC@}
+set SYSROOT_CFLAGS_FOR_TARGET {@SYSROOT_CFLAGS_FOR_TARGET@}
diff --git a/libgomp/testsuite/libgomp.c++/c++.exp b/libgomp/testsuite/libgomp.c++/c++.exp
index 8b4563b1d0d..ed096e17b9c 100644
--- a/libgomp/testsuite/libgomp.c++/c++.exp
+++ b/libgomp/testsuite/libgomp.c++/c++.exp
@@ -15,6 +15,10 @@ if { $blddir != "" } {
     verbose -log "GXX_UNDER_TEST not defined, will not execute c++ tests"
     return
 }
+if { $blddir != "" } {
+    set lang_source_re {^.*\.[cC]$}
+    set lang_include_flags [exec sh ${blddir}/../libstdc++-v3/scripts/testsuite_flags --build-includes]
+}
 lappend ALWAYS_CFLAGS "compiler=$GXX_UNDER_TEST"
 
 # If a testcase doesn't have special options, use these.
@@ -44,6 +48,8 @@ set_ld_library_path_env_vars
 dg-runtest $tests "" $DEFAULT_CFLAGS
 
 if { $blddir != "" } {
+    unset lang_source_re
+    unset lang_include_flags
     unset libstdc++_library_path
     unset lang_library_paths
 }
diff --git a/libgomp/testsuite/libgomp.oacc-c++/c++.exp b/libgomp/testsuite/libgomp.oacc-c++/c++.exp
index 79df401c99a..7b2315e406f 100644
--- a/libgomp/testsuite/libgomp.oacc-c++/c++.exp
+++ b/libgomp/testsuite/libgomp.oacc-c++/c++.exp
@@ -25,6 +25,10 @@ if { $blddir != "" } {
     verbose -log "GXX_UNDER_TEST not defined, will not execute c++ tests"
     return
 }
+if { $blddir != "" } {
+    set lang_source_re {^.*\.[cC]$}
+    set lang_include_flags [exec sh ${blddir}/../libstdc++-v3/scripts/testsuite_flags --build-includes]
+}
 lappend ALWAYS_CFLAGS "compiler=$GXX_UNDER_TEST"
 
 # Initialize dg.
@@ -121,6 +125,8 @@ foreach offload_target [concat [split $offload_targets ","] "disable"] {
 unset offload_target
 
 if { $blddir != "" } {
+    unset lang_source_re
+    unset lang_include_flags
     unset libstdc++_library_path
     unset lang_library_paths
 }