cares-compilers.m4: CARES_CONVERT_INCLUDE_TO_ISYSTEM adjustments

Add CARES_CHECK_COMPILER as a requirement.

Ensure macro does nothing unless GNU_C or CLANG compiler is used.

This should allow usage of this macro in unforeseen placements.

m4/cares-compilers.m4

@@ -15,7 +15,7 @@
 #***************************************************************************
 
 # File version for 'aclocal' use. Keep it a single number.
-# serial 66
+# serial 67
 
 
 dnl CARES_CHECK_COMPILER
@@ -418,6 +418,9 @@ dnl GNUC versions these warnings are not silenced.
 
 AC_DEFUN([CARES_CONVERT_INCLUDE_TO_ISYSTEM], [
   AC_REQUIRE([CARES_SHFUNC_SQUEEZE])dnl
+  AC_REQUIRE([CARES_CHECK_COMPILER])dnl
+  if test "$compiler_id" = "GNU_C" ||
+    test "$compiler_id" = "CLANG"; then
     tmp_has_include="no"
     tmp_chg_FLAGS="$CFLAGS"
     for word1 in $tmp_chg_FLAGS; do
@@ -448,6 +451,7 @@ AC_DEFUN([CARES_CONVERT_INCLUDE_TO_ISYSTEM], [
       CPPFLAGS="$tmp_chg_FLAGS"
       squeeze CPPFLAGS
     fi
+  fi
 ])