[build] reorder SUBDIRS to only recurse once

Currently, both GLX and GLdispatch recurse into src/util/trace.  This causes
problems for parallel make, and breaks distclean because the first recursion
into src/util/trace deletes the Makefile, causing the second recursion to fail.

Instead, recurse directly into util from src/Makefile.am, putting it ahead of
both GLX and GLdispatch in SUBDIRS.  This means that you can't just go into
src/GLX and type make, but it fixes parallel builds and distclean.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
[build] fix srcdir != builddir mistakes

When configure is run from a directory other than the source directory, various
files fail to compile because the include paths use $(builddir) or
$(top_builddir) when the source is actually in $(srcdir) or $(top_srcdir).

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