scons: Fix dependencies of marshal_generated.[ch].
scons: Fix dependencies of marshal_generated.[ch].

These generated source files depend not only upon gl_and_es_API.xml, but
all other XML files that are included by it.

This change updates the generation rules to depend on all gen/*.xml
files, like done for other SCons generation rules, and should fix
incremental broken SCons builds due to missing dependencies.

Trivial.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler