microblaze port

based on initial work by rdp, with heavy modifications. some features
including threads are untested because qemu app-level emulation seems
to be broken and I do not have a proper system image for testing.
diff --git a/configure b/configure
index 93518a7..2969b95 100755
--- a/configure
+++ b/configure
@@ -202,6 +202,7 @@
 i?86*) ARCH=i386 ;;
 x86_64*) ARCH=x86_64 ;;
 mips-*|mipsel-*) ARCH=mips ;;
+microblaze-*) ARCH=microblaze ;;
 unknown) fail "$0: unable to detect target arch; try $0 --target=..." ;;
 *) fail "$0: unknown or unsupported target \"$target\"" ;;
 esac