[PATCH] testsuite: Fix bad-mapper-1.C test failures with posix_spawn

bad-mapper-1.C has been failing since the posix_spawn codepath was added
to libiberty, adjust the check to accept the changed error message.

Patch has been verified on x86_64 Linux.

gcc/testsuite:

	* g++.dg/modules/bad-mapper-1.C: Also accept posix_spawn.

gcc/testsuite/g++.dg/modules/bad-mapper-1.C

 //  { dg-additional-options "-fmodules-ts -fmodule-mapper=|this-will-not-work" }
 import unique1.bob;
-// { dg-error "-:failed (exec|CreateProcess).*mapper.* .*this-will-not-work" "" { target { ! { *-*-darwin[89]* *-*-darwin10* } } } 0 }
+// { dg-error "-:failed (exec|CreateProcess|posix_spawn).*mapper.* .*this-will-not-work" "" { target { ! { *-*-darwin[89]* *-*-darwin10* } } } 0 }
 // { dg-prune-output "fatal error:" }
 // { dg-prune-output "failed to read" }
 // { dg-prune-output "compilation terminated" }