CMakeLists: build reproducible by default
CMakeLists: build reproducible by default

Using the build user and build hostname as part of the git hash breaks
reproducible builds. Make this part optional, but build reproducible by
default.

sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets