Use ppc host calling convention definitions to set TCG_TARGET_CALL_{ALIGN_ARGS,STACK_OFFSET}.

New version after malc's comments.  (This avoids having to do
  #if defined __linux__ || defined __FreeBSD__ || defined __FreeBSD_kernel__
for the third case.)

Submitted by: Andreas Tobler <andreast@fgznet.ch>  (original version)
Signed-off-by: NJuergen Lock <nox@jelal.kn-bremen.de>
Signed-off-by: Nmalc <av1474@comtv.ru>

tcg/ppc/tcg-target.h

@@ -65,11 +65,11 @@ enum {
 /* used for function call generation */
 #define TCG_REG_CALL_STACK TCG_REG_R1
 #define TCG_TARGET_STACK_ALIGN 16
-#if defined __APPLE__
+#if defined _CALL_DARWIN
 #define TCG_TARGET_CALL_STACK_OFFSET 24
-#elif defined _AIX
+#elif defined _CALL_AIX
 #define TCG_TARGET_CALL_STACK_OFFSET 52
-#elif defined __linux__
+#elif defined _CALL_SYSV
 #define TCG_TARGET_CALL_ALIGN_ARGS 1
 #define TCG_TARGET_CALL_STACK_OFFSET 8
 #else