Can't build v6.15.0 on macOS Mojave

[hyj1991]

• Version: v6.15.0
• Platform: macOS Mojave 10.14.1
• Subsystem: Xcode 10.1（Build version 10B61）

Error message:

In file included from ../deps/icu-small/source/common/stringtriebuilder.cpp:17:
../deps/icu-small/source/common/utypeinfo.h:30:10: fatal error: 'typeinfo' file not found
#include <typeinfo>  // for 'typeid' to work
         ^~~~~~~~~~
1 warning and 1 error generated.
make[1]: *** [/Users/yijun/git/node/out/Release/obj.target/icuucx/deps/icu-small/source/common/stringtriebuilder.o] Error 1
rm 12efedf49e7893a8bf1719ba795654e432c54d73.intermediate
make: *** [node] Error 2

[richardlau]

See #24648. Apple have changed things in Xcode 10.1 which we cannot workaround for Node.js 6 without risking breaking compatibility.