If the system we're building Epoxy on has GL and EGL pkg-config modules,
then we should add them to the Requires.private field of the pkg-config
file.
The Requires.private field does not contribute to the linker flags
generated by pkg-config, unless we're doing a static build; it does,
however, contribute to the compiler flags generated by pkg-config, which
means that platforms that specify ad hoc compiler flags for their GL and
EGL implementations via pkg-config will be able to propagate them
through Epoxy.
Closes: #139
Since Epoxy can be built with different platform-specific API, having a
way for dependent projects to discover those capabilities without
necessarily crashing the minute they attempt to use them is a good
feature to have.
We strongly direct library and application developers to use pkg-config
in order to use Epoxy, so it makes sense to add variables to the
epoxy.pc file that can be easily extracted at configuration time.
The new linker requires that the consumers of a library link against
the libraries that that library depends on, which is supported by
Libs.private.
Fixes#16
Emmanuele Bassi
Eric Anholt