testsuite: Allow general skips/requires in PCH tests

dg-pch.exp handled dg-require-effective-target pch_supported_debug
as a special case, by grepping the source code.  This patch tries
to generalise it to other dg-require-effective-targets, and to
dg-skip-if.

There also seemed to be some errors in check-flags.  It used:

    lappend $args [list <elt>]

which treats the contents of args as a variable name.  I think
it was supposed to be "lappend args" instead.  From the later
code, the element was supposed to be <elt> itself, rather than
a singleton list containing <elt>.

We can also save some time by doing the common early-exit first.

Doing this removes the need to specify the dg-require-effective-target
in both files.  Tested by faking unsupported debug and checking that
the tests were still correctly skipped.

gcc/testsuite/
	* lib/target-supports-dg.exp (check-flags): Move default argument
	handling further up.  Fix a couple of issues in the lappends.
	Avoid frobbing the compiler flags if the return value is already
	known to be 1.
	* lib/dg-pch.exp (dg-flags-pch): Process the dg-skip-if and
	dg-require-effective-target directives to see whether the
	assembly test should be skipped.
	* gcc.dg/pch/valid-1.c: Remove dg-require-effective-target.
	* gcc.dg/pch/valid-1b.c: Likewise.

gcc/testsuite/gcc.dg/pch/valid-1.c

@@ -1,4 +1,3 @@
-/* { dg-require-effective-target pch_supported_debug } */
 /* { dg-options "-I. -Winvalid-pch -g" } */
 
 #include "valid-1.h"/* { dg-warning "created with .none. debug info, but used with" } */

gcc/testsuite/gcc.dg/pch/valid-1b.c

@@ -1,4 +1,3 @@
-/* { dg-require-effective-target pch_supported_debug } */
 /* { dg-options "-I. -Winvalid-pch -g0" } */
 
 #include "valid-1b.h"

gcc/testsuite/lib/dg-pch.exp

@@ -100,6 +100,27 @@ proc dg-flags-pch { subdir test otherflags options suffix } {
 	# For the rest, the default is to compile to .s.
 	set dg-do-what-default compile
 
+	# Process the target selectors to see whether the remaining
+	# part of the test should be skipped.
+	#
+	# ??? This doesn't currently handle flag-specific skips,
+	# based on dg-options.
+	set dg-do-what [list compile "" P]
+	set dg-extra-tool-flags ""
+	foreach op [dg-get-options "./$bname$suffix"] {
+	    switch [lindex $op 0] {
+		dg-require-effective-target -
+		dg-skip-if {
+		    if { [catch "$op" msg] } {
+			perror "$bname$suffix: $msg for \"$op\""
+		    }
+		}
+	    }
+	}
+	if { [lindex ${dg-do-what} 1] == "N" } {
+	    continue
+	}
+
 	set have_errs [llength [grep $test "{\[ \t\]\+dg-error\[ \t\]\+.*\[ \t\]\+}"]]
 
 	if { [ file_on_host exists "$bname$suffix.gch" ] } {
@@ -134,8 +155,7 @@ proc dg-flags-pch { subdir test otherflags options suffix } {
  		    fail "$nshort $flags assembly comparison"
 		}
 	    }
-	} elseif { $pch_unsupported_debug == 0 \
-		   || [llength [grep $test "{\[ \t\]\+dg-require-effective-target\[ \t\]\+pch_supported_debug\[ \t\]\+.*\[ \t\]\+}"]] > 0 } {
+	} else {
 	    verbose -log "pch file '$bname$suffix.gch' missing"
 	    fail "$nshort $flags"
 	    if { !$have_errs } {

gcc/testsuite/lib/target-supports-dg.exp

@@ -334,6 +334,23 @@ proc check-flags { args } {
     # The args are within another list; pull them out.
     set args [lindex $args 0]
 
+    # The next two arguments are optional.  If they were not specified,
+    # use the defaults.
+    if { [llength $args] == 2 } {
+	lappend args "*"
+    }
+    if { [llength $args] == 3 } {
+	lappend args ""
+    }
+
+    # If the option strings are the defaults, or the same as the
+    # defaults, there is no need to call check_conditional_xfail to
+    # compare them to the actual options.
+    if { [string compare [lindex $args 2] "*"] == 0
+	 && [string compare [lindex $args 3] "" ] == 0 } {
+	return 1
+    }
+
     # Start the list with a dummy tool name so the list will match "*"
     # if there are no flags.
     set compiler_flags " toolname "
@@ -350,26 +367,9 @@ proc check-flags { args } {
 	append compiler_flags "[board_info $dest multilib_flags] "
     }
 
-    # The next two arguments are optional.  If they were not specified,
-    # use the defaults.
-    if { [llength $args] == 2 } {
-	lappend $args [list "*"]
-    }
-    if { [llength $args] == 3 } {
-	lappend $args [list ""]
-    }
-
-    # If the option strings are the defaults, or the same as the
-    # defaults, there is no need to call check_conditional_xfail to
-    # compare them to the actual options.
-    if { [string compare [lindex $args 2] "*"] == 0
-	 && [string compare [lindex $args 3] "" ] == 0 } {
-	set result 1    
-    } else {
-	# The target list might be an effective-target keyword, so replace
-	# the original list with "*-*-*", since we already know it matches.
-	set result [check_conditional_xfail [lreplace $args 1 1 "*-*-*"]]
-    }
+    # The target list might be an effective-target keyword, so replace
+    # the original list with "*-*-*", since we already know it matches.
+    set result [check_conditional_xfail [lreplace $args 1 1 "*-*-*"]]
 
     # Any value in this variable was left over from an earlier test.
     set compiler_flags ""