travis: Parse configure.ac to pick an updated LIBDRM_VERSION.
travis: Parse configure.ac to pick an updated LIBDRM_VERSION.

Travis has been broken a couple of times by configure.ac updates.  To make
it useful, auto-update the version necessary.

This could potentially be used for other dependencies, too, but those get
bumped less frequently.

Reviewed-by: Emil Velikov <f20878473f414da183da19ee25c8722cc1d711e4@collabora.com>
Reviewed-by: Rhys Kidd <0b3b315d08353e2046d43a86d41e3fd1dff3d6ad@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler