Change __PPC__ define to __powerpc__.

diff --git a/include/basetsd.h b/include/basetsd.h
index 81ada05..615b371 100644
--- a/include/basetsd.h
+++ b/include/basetsd.h
@@ -131,7 +131,7 @@
 # define WORDS_BIGENDIAN
 # define BITFIELDS_BIGENDIAN
 # undef  ALLOW_UNALIGNED_ACCESS
-#elif defined(__PPC__)
+#elif defined(__powerpc__)
 # define WORDS_BIGENDIAN
 # define BITFIELDS_BIGENDIAN
 # undef  ALLOW_UNALIGNED_ACCESS