dejagnu: modularize gcc-dg-debug-runtest a bit

Move some functionality into a procedure of its own. This is only so that when
the patch for ctf comes along, the gcc-dg-debug-runtest procedure looks bit
more uniform.

gcc/testsuite/ChangeLog:

	* lib/gcc-dg.exp (gcc-dg-target-supports-debug-format): New procedure.

gcc/testsuite/lib/gcc-dg.exp

@@ -621,18 +621,27 @@ proc gcc-dg-runtest { testcases flags default-extra-flags } {
     }
 }
 
-proc gcc-dg-debug-runtest { target_compile trivial opt_opts testcases } {
+# Check if the target system supports the debug format
+proc gcc-dg-target-supports-debug-format { target_compile trivial type } {
     global srcdir subdir
 
+    set comp_output [$target_compile \
+	    "$srcdir/$subdir/$trivial" "trivial.S" assembly \
+	    "additional_flags=$type"]
+    if { ! [string match "*: target system does not support the * debug format*" \
+	    $comp_output] } {
+	remove-build-file "trivial.S"
+	return 1
+    }
+    return 0
+}
+
+proc gcc-dg-debug-runtest { target_compile trivial opt_opts testcases } {
     if ![info exists DEBUG_TORTURE_OPTIONS] {
 	set DEBUG_TORTURE_OPTIONS ""
 	foreach type {-gdwarf-2 -gstabs -gstabs+ -gxcoff -gxcoff+} {
-	    set comp_output [$target_compile \
-		    "$srcdir/$subdir/$trivial" "trivial.S" assembly \
-		    "additional_flags=$type"]
-	    if { ! [string match "*: target system does not support the * debug format*" \
-		    $comp_output] } {
-		remove-build-file "trivial.S"
+	    if [expr [gcc-dg-target-supports-debug-format \
+		      $target_compile $trivial $type]] {
 		foreach level {1 "" 3} {
 		    if { ($type == "-gdwarf-2") && ($level != "") } {
 			lappend DEBUG_TORTURE_OPTIONS [list "${type}" "-g${level}"]