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/bswap.h b/bswap.h
index 08b77d9..63b81cc 100644
--- a/bswap.h
+++ b/bswap.h
@@ -134,7 +134,7 @@
 
 /* unaligned versions (optimized for frequent unaligned accesses)*/
 
-#if defined(__i386__) || defined(__powerpc__)
+#if defined(__i386__) || defined(_ARCH_PPC)
 
 #define cpu_to_le16wu(p, v) cpu_to_le16w(p, v)
 #define cpu_to_le32wu(p, v) cpu_to_le32w(p, v)