All dependencies were using find_library, has_header, get_define, etc on
self.compiler assuming that it's a compiler that outputs and consumes
C-like libraries. This is not true for D (and in the future, for Rust)
since although they can consume C libraries, they do not use the
C ecosystem.
For such purposes, we now have self.clib_compiler. Nothing uses
self.compiler anymore as a result, and it has been removed.
pypy installations don't usuallyy ship with pkg-config files,
we thus need to replicate what their version of distutils does.
In addition, we also try our best to build against other
pythons that do not have pkg-config files.
What is actually defined here varies wildly on different python-versions
for different platforms.
On my python2.7 on Windows len(sysconfig.get_config_vars()) returns 17,
whereas in my Ubuntu that number is 517!
Hence it is useful to be able to check which keys are available, as
well as allowing specifying a default option.
Nirbheek Chauhan
Salamandar
Mathieu Duponchelle
Havard Graff
Jussi Pakkanen