powerpc: enhance 32/64bit detection

We were using uname to determine if userspace was 32 or 64bit.
This fails when we have a 64bit kernel and a 32bit userspace.

* configure.ac (powerpc*): Similar to x86, use a runtime test
to determine if we are 32 or 64bit.

Signed-off-by: Anton Blanchard <anton@samba.org>
diff --git a/configure.ac b/configure.ac
index 03e49fe..b3b62e8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -54,7 +54,11 @@
 powerpc*)
 	arch=powerpc
 	AC_DEFINE([POWERPC], 1, [Define for the PowerPC architecture.])
-	if test $host_cpu = powerpc64; then
+	AC_TRY_COMPILE(
+[#ifndef __LP64__
+# error 32 bit
+#endif], [], ppc_bits=64, ppc_bits=32)
+	if test "$ppc_bits" = "64"; then
 		AC_DEFINE([POWERPC64], 1, [Define for the PowerPC64 architecture.])
 	fi
 	;;