configure: use standard check for attribure alias
configure: use standard check for attribure alias

Currently we have two macros - HAVE_ALIAS and GLX_ALIAS_UNSUPPORTED.
To make it even better former of which is explicitly cleared in some
cases while not in others.

Clear all that up by using a single macro properly set during configure.

Signed-off-by: Emil Velikov <f20878473f414da183da19ee25c8722cc1d711e4@collabora.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler