glapi/glx: Treat xserver generated targets as .PHONY
glapi/glx: Treat xserver generated targets as .PHONY

Meaning, always rebuild them when asked instead of bothering to look at
timestamps (and then wondering why nothing happened when you said make).

Reviewed-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>
Signed-off-by: Adam Jackson <4482611cc290c2ce1399431891dcb9221c95f994@redhat.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler