tools/cmake: fix compile on Alpine Linux

tools/cmake: fix compile on Alpine Linux

internal jsoncpp include order leads to multiple build
errors on Alpine Linux which uses musl libc

use include order from upstream jsoncpp

first error was:
In file included from /usr/include/c++/5.3.0/stdexcept:38:0,
                 from /home/..../openwrt/build_dir/host/cmake-3.4.3/Utilities/cmjsoncpp/include/json/assertions.h:16,
                 from /home/..../openwrt/build_dir/host/cmake-3.4.3/Utilities/cmjsoncpp/src/lib_json/json_reader.cpp:7:
/usr/include/c++/5.3.0/exception:35:9: error: '#pragma' is not allowed here
 #pragma GCC visibility push(default)

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@48995 3c298f89-4303-0410-b956-a3cf2f4a3e73