Metaware's High-C has an ISO cpp.

include/curl/curl.h

@@ -485,7 +485,7 @@ typedef enum {
  */
 #if defined(__STDC__) || defined(_MSC_VER) || defined(__cplusplus) || \
   defined(__HP_aCC) || defined(__BORLANDC__) || defined(__LCC__) || \
-  defined(__POCC__) || defined(__SALFORDC__)
+  defined(__POCC__) || defined(__SALFORDC__) || defined(__HIGHC__)
   /* This compiler is believed to have an ISO compatible preprocessor */
 #define CURL_ISOCPP
 #else