This allows to pass include paths and flags only to a given thirdparty
library, thus preventing conflicts between their files (e.g. between
opus and openssl which both provide modes.h.
This also has the nice effect of making the compilation command smaller
for each module as it no longer related to all other modules, only the
final linking brings them together.
This however requires adding manually the ogg include path in opus
and vorbis when building against the builtin ogg, since it is no longer
in the global env.
Also simplified template 'thirdparty_<module>_sources' to
'thirdparty_sources'.
"Core" modules like cscript, gdscript, gridmap, ik and virtual_script
still use the main env_modules, but it could be changed if need be.
(cherry picked from commit da09c6131b)
Obviously removed the parts about enet and visual_script.
Took the opportunity to undo the Godot changed made to the
opus source. The opus module should eventually be built in its
own environment to avoid polluting others with too many include
dirs and defines.
TODO: Fix the platform/ stuff for opus.
(cherry picked from commit d9a291f641)
speex module was only added while cherry-picking, as speex is removed
in the master branch but we don't want to break compatibility in 2.1.x.
Unbundling wasn't done as the module uses the internal speex_free,
so it would require some more work.
