Improve sorry message for -fzero-call-used-regs

When the -fzero-call-used-regs command line option is used with an
unsupported value, indicate that it's a value problem instead of an
option problem.

Without the patch, the error is:
In file included from gcc/testsuite/c-c++-common/zero-scratch-regs-8.c:5:
gcc/testsuite/c-c++-common/zero-scratch-regs-1.c: In function 'foo':
gcc/testsuite/c-c++-common/zero-scratch-regs-1.c:10:1: sorry, unimplemented: '-fzero-call-used-regs' not supported on this target
   10 | }
      | ^

With the patch, the error would be like this:
 In file included from gcc/testsuite/c-c++-common/zero-scratch-regs-8.c:5:
gcc/testsuite/c-c++-common/zero-scratch-regs-1.c: In function 'foo':
gcc/testsuite/c-c++-common/zero-scratch-regs-1.c:10:1: sorry, unimplemented: argument 'all-arg' is not supported for '-fzero-call-used-regs' on this target
   10 | }
      | ^

2022-09-19  Torbjörn SVENSSON  <torbjorn.svensson@foss.st.com>

gcc/ChangeLog:

	* targhooks.cc (default_zero_call_used_regs): Improve sorry
	message.

Signed-off-by: Torbjörn SVENSSON  <torbjorn.svensson@foss.st.com>

gcc/targhooks.cc

@@ -93,6 +93,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple.h"
 #include "cfgloop.h"
 #include "tree-vectorizer.h"
+#include "options.h"
 
 bool
 default_legitimate_address_p (machine_mode mode ATTRIBUTE_UNUSED,
@@ -1181,9 +1182,21 @@ default_zero_call_used_regs (HARD_REG_SET need_zeroed_hardregs)
       static bool issued_error;
       if (!issued_error)
 	{
+	  const char *name = NULL;
+	  for (unsigned int i = 0; zero_call_used_regs_opts[i].name != NULL;
+	       ++i)
+	    if (flag_zero_call_used_regs == zero_call_used_regs_opts[i].flag)
+	      {
+		name = zero_call_used_regs_opts[i].name;
+		break;
+	      }
+
+	  if (!name)
+	    name = "";
+
 	  issued_error = true;
-	  sorry ("%qs not supported on this target",
-		 "-fzero-call-used-regs");
+	  sorry ("argument %qs is not supported for %qs on this target",
+		 name, "-fzero-call-used-regs");
 	}
     }