Remove all traces of __powerpc__

According to $GCC/gcc/config/rs6000/rs6000-c.c _ARCH_PPC is the
ubiquitous define which should be used to test whether gcc targets
PowerPC, on 64bit platforms _ARCH_PPC64 will be also defined.

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6301 c046a42c-6fe2-441c-8c8c-71466251a162
diff --git a/tcg/tcg.h b/tcg/tcg.h
index e83073b..323cc52 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -457,7 +457,7 @@
 uint64_t tcg_helper_remu_i64(uint64_t arg1, uint64_t arg2);
 
 extern uint8_t code_gen_prologue[];
-#if defined(__powerpc__) && !defined(__powerpc64__)
+#if defined(_ARCH_PPC) && !defined(_ARCH_PPC64)
 #define tcg_qemu_tb_exec(tb_ptr) \
     ((long REGPARM __attribute__ ((longcall)) (*)(void *))code_gen_prologue)(tb_ptr)
 #else