Fix target detection on mingw32

gcc -dumpmachine returns only 'mingw32'

Change-Id: I774d05a97c5131fc12009e436712c319e54490a5

build/make/configure.sh

@@ -518,6 +518,7 @@ process_common_toolchain() {
                 tgt_os=darwin9
                 ;;
             *mingw32*|*cygwin*)
+                [ -z "$tgt_isa" ] && tgt_isa=x86
                 tgt_os=win32
                 ;;
             *linux*|*bsd*)