[PATCH, AIX] Add missing macros PR39950

[David Edelsohn]

The appended patch adds a few macros that XLC now defines on AIX.

- David

        * config/rs6000/aix.h (TARGET_OS_AIX_CPP_BUILTINS): Define
        __powerpc__, __PPC__, __unix__.

Index: aix.h
===================================================================
--- aix.h       (revision 179610)
+++ aix.h       (working copy)
@@ -97,6 +97,9 @@
     {                                          \
       builtin_define ("_IBMR2");               \
       builtin_define ("_POWER");               \
+      builtin_define ("__powerpc__");           \
+      builtin_define ("__PPC__");               \
+      builtin_define ("__unix__");              \
       builtin_define ("_AIX");                 \
       builtin_define ("_AIX32");               \
       builtin_define ("_AIX41");               \