8338108: Give better error message in configure if a full XCode is missing

Reviewed-by: jwaters, erikj, shade

make/autoconf/toolchain.m4

@@ -678,6 +678,9 @@ AC_DEFUN_ONCE([TOOLCHAIN_DETECT_TOOLCHAIN_EXTRA],
       test_metal=`$METAL --version 2>&1`
       if test $? -ne 0; then
         AC_MSG_RESULT([no])
+        AC_MSG_NOTICE([A full XCode is required to build the JDK (not only command line tools)])
+        AC_MSG_NOTICE([If you have XCode installed, you might need to reset the Xcode active developer directory])
+        AC_MSG_NOTICE([using 'sudo xcode-select -r'])
         AC_MSG_ERROR([XCode tool 'metal' neither found in path nor with xcrun])
       else
         AC_MSG_RESULT([yes, will be using '$METAL'])