cmake: get language from Meson project if not specified as depedency(..., langugage: ...)
deps: add threads method:cmake
dependency('threads', method: 'cmake') is useful for cmake unit tests
or those who just want to find threads using cmake.
cmake: project(... Fortran) generally also requires C language
It turns out there's a bug in creating a sub dependency out of threads
in that we pass all of the kwargs from the parent to the
ThreadDependency instance. This demonstrates the bug.