Check -fcf-protection

* configure.ac: Check if CFLAGS actually includes -fcf-protection
  instead of checking if the flag is valid by RUBY_TRY_CFLAGS.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65819 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.ac

@@ -1002,8 +1002,7 @@ main()
 			ac_cv_func___builtin_setjmp=no
 		])
 		# With gcc-8's -fcf-protection, MJIT's __builtin_longjmp fails.
-		# TODO: Check if CFLAGS actually includes -fcf-protection instead of using RUBY_TRY_CFLAGS
-		RUBY_TRY_CFLAGS(-fcf-protection, [cf_protection=yes], [cf_protection=no])
+		AS_CASE(["$CC $CFLAGS "], [*" -fcf-protection "*], [cf_protection=yes], [cf_protection=no])
 		AS_IF([test "$cf_protection" = yes], [
 			ac_cv_func___builtin_setjmp=no
 		])