arch/strarg: provide the stdarg implementation for greenhills compiler

the greenhills compiler provide its own implementation of va_start,
va_end, va_arg, va_copy. so if we are build vela with greenhills
compiler, we should using the stdarg implementation provided by
greenhills, not our own

Signed-off-by: guoshichao <guoshichao@xiaomi.com>

arch/arm/include/stdarg.h

@@ -25,6 +25,10 @@
  * Included Files
  ****************************************************************************/
 
+#ifdef __ghs__
+#  include <ansi/stdarg.h>
+#else
+
 /****************************************************************************
  * Pre-processor Prototypes
  ****************************************************************************/
@@ -42,4 +46,6 @@
 
 typedef __builtin_va_list va_list;
 
+#endif
+
 #endif /* __ARCH_ARM_INCLUDE_STDARG_H */