configure.in: Try to determine CRT_DIR automatically when using gcc

ChangeLog

@@ -1,3 +1,8 @@
+2011-06-16  Miles Bader <miles@gnu.org>
+
+	* configure.in: Try to determine CRT_DIR automatically when
+	using gcc.
+
 2011-06-15  Paul Eggert  <eggert@cs.ucla.edu>
 
 	* lib/ftoastr.c, lib/stdio.in.h, lib/verify.h:

configure.in

@@ -988,6 +988,21 @@ dnl Do this early because it can frob feature test macros for Unix-98 &c.
 AC_SYS_LARGEFILE
 
 
+## If we're using gcc, and the user hasn't specified a crt-dir, try to
+## determine it automatically by asking gcc.  [If this doesn't work,
+## CRT_DIR will remain empty and system-dependent code will be used
+## below.]
+##
+if test "x${GCC}z$CRT_DIR" = xyesz; then
+   crt_file=`$CC 2>/dev/null --print-file-name=crt1.o`
+   case "$crt_file" in
+     */*)
+       CRT_DIR=`AS_DIRNAME(["$crt_file"])`
+       ;;
+   esac
+fi
+
+
 ## If user specified a crt-dir, use that unconditionally.
 if test "X$CRT_DIR" = "X"; then