toolchain/ghs: Fix green hills toolchain build Vela "no storage class…

… or type specifier" error

"libcxxmini/libxx_cxa_guard.cxx", line 47: error apache#77-D: this declaration has
          no storage class or type specifier
  __extension__ typedef int __guard __attribute__((mode(__DI__)));
  ^

"libcxxmini/libxx_cxa_guard.cxx", line 47: error apache#65: expected a ";"
  __extension__ typedef int __guard __attribute__((mode(__DI__)));
                ^

"libcxxmini/libxx_cxa_guard.cxx", line 64: error apache#20: identifier "__guard" is
          undefined
    int __cxa_guard_acquire(FAR __guard *g)
                                ^

"libcxxmini/libxx_cxa_guard.cxx", line 64: error apache#20: identifier "g" is
          undefined
    int __cxa_guard_acquire(FAR __guard *g)
                                         ^

"libcxxmini/libxx_cxa_guard.cxx", line 65: error apache#65: expected a ";"
    {
    ^

"libcxxmini/libxx_cxa_guard.cxx", line 93: warning apache#12-D: parsing restarts
          here after previous syntax error
  }

Signed-off-by: yanghuatao <[email protected]>

include/nuttx/compiler.h

@@ -1036,6 +1036,12 @@
 
 #  define no_builtin(n)
 
+/* Green Hills Software definitions *****************************************/
+
+#elif defined(__ghs__)
+
+#  define __extension__
+
 /* Unknown compiler *********************************************************/
 
 #else