build: Add -static for mingw builds

This avoids a dependency on libssp-0.dll when built with
-fstack-protector-all.

configure.ac

@@ -175,6 +175,7 @@ case $host in
      AC_CHECK_LIB([iphlpapi],      [main],, AC_MSG_ERROR(lib missing))
      AC_CHECK_LIB([crypt32],      [main],, AC_MSG_ERROR(lib missing))
 
+     AX_CHECK_LINK_FLAG([[-static]],[LDFLAGS="$LDFLAGS -static"])
      AX_CHECK_LINK_FLAG([[-static-libgcc]],[LDFLAGS="$LDFLAGS -static-libgcc"])
      AX_CHECK_LINK_FLAG([[-static-libstdc++]],[LDFLAGS="$LDFLAGS -static-libstdc++"])