Do not rely on __powerpc__ being defined as a feature test macro

__powerpc__ is not defined on AIX and Darwin, Makefile.target adds
it to CPPFLAGS for target specific code which cache-utils are not.

Since there's not common definition which can safely be used on all
platforms use HOST_PPC provided by config-host.h

The problem was originally reported by C. W. Betts

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6292 c046a42c-6fe2-441c-8c8c-71466251a162

cache-utils.c

 #include "cache-utils.h"
 
-#ifdef __powerpc__
+#ifdef HOST_PPC
 struct qemu_cache_conf qemu_cache_conf = {
     .dcache_bsize = 16,
     .icache_bsize = 16
@@ -68,4 +68,4 @@ void qemu_cache_utils_init(char **envp)
 }
 #endif
 
-#endif /* __powerpc__ */
+#endif /* HOST_PPC */

cache-utils.h

 #ifndef QEMU_CACHE_UTILS_H
 #define QEMU_CACHE_UTILS_H
 
-#ifdef __powerpc__
+#include "config-host.h"
+
+#ifdef HOST_PPC
 struct qemu_cache_conf {
     unsigned long dcache_bsize;
     unsigned long icache_bsize;