Add PowerPC processor detection.

diff --git a/configure.ac b/configure.ac
index 369205a..32f897b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1314,6 +1314,7 @@
   *i[[3456789]]86*) WINE_CHECK_DEFINE([__i386__]) ;;
   *alpha*)          WINE_CHECK_DEFINE([__ALPHA__]) ;;
   *sparc*)          WINE_CHECK_DEFINE([__sparc__]) ;;
+  *powerpc*)        WINE_CHECK_DEFINE([__powerpc__]) ;;
 esac
 
 case $host_vendor in