Move CCompiler.compile to Compiler.compile so that ValaCompiler can use
it. Also rewrite ValaCompiler.sanity_check to use it since it does
a simple compile check.
At the same time, it enhances ExternalLibrary to support arguments for
languages other than C-like.
Includes a test for this that links against zlib through Vala.
Closes#983
Since Vala require 'glib-2.0' and 'gobject-2.0' dependencies, it's
better to fail at 'valac' step with meaningful error.
Add missing 'gobject-2.0' dependency on the mixed source test case.
Not only does extract_all_objects() now work properly again,
extract_objects() also works if you specify a subset of sources all of
which have been compiled into a single unified object.
So, for instance, this allows you to extract all the objects
corresponding to the C sources compiled into a target consisting of
C and C++ sources.
This is the first step in making Vala support have feature-parity with
C/C++ support. Vala and Vapi sources generated with Generators and
CustomTargets are no longer ignored. Dependencies are setup properly and
they are added to the commandline.