configure: Allow command-line configure for ppc32

Similar to manually selecting i386 for an x86_64 host.

Signed-off-by: Richard Henderson <rth@twiddle.net>
diff --git a/configure b/configure
index 05e16da..ef4d9bf 100755
--- a/configure
+++ b/configure
@@ -981,6 +981,14 @@
 done
 
 case "$cpu" in
+    ppc)
+           CPU_CFLAGS="-m32"
+           LDFLAGS="-m32 $LDFLAGS"
+           ;;
+    ppc64)
+           CPU_CFLAGS="-m64"
+           LDFLAGS="-m64 $LDFLAGS"
+           ;;
     sparc)
            LDFLAGS="-m32 $LDFLAGS"
            CPU_CFLAGS="-m32 -mcpu=ultrasparc"