[build] fix more srcdir != builddir mistakes

I missed these in commit debae590e724ee064939982bd3f54a613d5fa650 because my
test system had a compatible glxext.h in /usr/include/GL.  On a system with an
incompatible version (i.e. Ubuntu), this causes build failures.  Fix the include
paths to include the GL headers from the repository instead of the system.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Signed-off-by: Brian Nguyen <brnguyen@nvidia.com>
[build] don't try to create src/GLdispatch/mapi makefiles

The build doesn't recurse into these directories, so their Makefile.in files
aren't propagated to the dist tarball.  That makes configure fail because it
tries to read those files to generate Makefiles in those directories.

Since these directories aren't built, don't try to create Makefiles in them.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
[build] make mapi a subdirectory of vnd-glapi

Currently, the GLdispatch makefile recurses into the mapi/vnd-glapi
subdirectory, which then uses files out of its parent directory.  This makes it
difficult to include the mapi directory in the dist tarball because just
including it in EXTRA_DIST makes it pick up the generated Makefile in addition
to the checked-in source files.

Instead, exchange the two directories so that mapi is a subdirectory of
vnd-glapi and the former is included wholesale with EXTRA_DIST.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
[build] distribute files needed to build

Everything needed to actually build the driver needs to be included in something
that makes it end up in the distribution tarball.  For headers, use
noinst_HEADERS.  For everything else, use EXTRA_DIST.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
[build] add $(BUILT_SOURCES) to $(CLEANFILES)

The 'distclean' target should completely cleans the build directory, so that
$(builddir) contains only directories.  This means that all built sources have
to be included in CLEANFILES, or they're left behind.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>