Set MOZ_JS_LIBS properly for win32 gcc builds.

Bug #371236 r=bsmedberg

configure.in

@@ -1763,6 +1763,7 @@ case "$target" in
         RCFLAGS='-O coff --use-temp-file'
         # mingw doesn't require kernel32, user32, and advapi32 explicitly
         LIBS="$LIBS -lgdi32 -lwinmm -lwsock32"
+        MOZ_JS_LIBS='-L$(LIBXUL_DIST)/lib -ljs$(MOZ_BITS)$(VERSION_NUMBER)'
         MOZ_FIX_LINK_PATHS=
         DYNAMIC_XPCOM_LIBS='-L$(LIBXUL_DIST)/lib -lxpcom -lxpcom_core'
         XPCOM_FROZEN_LDOPTS='-L$(LIBXUL_DIST)/lib -lxpcom'