Remove powerpc* optimisations, they're full of gcc-isms

Index: m4/as-host-defines.m4
--- m4/as-host-defines.m4.orig
+++ m4/as-host-defines.m4
@@ -19,10 +19,6 @@ AC_DEFUN([AS_HOST_DEFINES],
       HAVE_AMD64=yes
       AC_DEFINE(HAVE_AMD64, 1, [Defined if host is amd64])
       ;;
-    xpowerpc|xppc|xpowerpc64|xppc64)
-      HAVE_POWERPC=yes
-      AC_DEFINE(HAVE_POWERPC, 1, [Defined if host is powerpc])
-      ;;
     xarm)
       HAVE_ARM=yes
       AC_DEFINE(HAVE_ARM, 1, [Defined if host is arm])