internal.h: add BUILTIN_NOT_REACHED macro for VS compiler
internal.h: add BUILTIN_NOT_REACHED macro for VS compiler

ghaderer/libmicrohttpd,maru/libmicrohttpd-http2,maru/libmicrohttpd-http2,ghaderer/libmicrohttpd,maru/libmicrohttpd-http2,ghaderer/libmicrohttpd