dl-string.h: use __powerpc__ guard instead of powerpc

powerpc guard depends on the compiler options, __powerpc__ should
work all the time.

Signed-off-by: Peter S. Mazinger <ps.m@gmx.net>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

ldso/include/dl-string.h

@@ -142,7 +142,7 @@ static __always_inline int _dl_memcmp(const void *s1, const void *s2, size_t len
 	return 0;
 }
 
-#if defined(powerpc)
+#if defined(__powerpc__)
 /* Will generate smaller and faster code due to loop unrolling.*/
 static __always_inline void * _dl_memset(void *to, int c, size_t n)
 {