meson: build classic osmesa

This builds the classic (non-gallium) osmesa with meson. This has been
tested with the osdemo application from mesa-demos.

v2: - Remove unrelated change
    - Add SELinux dependency to osmesa

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>

include/meson.build

@@ -55,7 +55,7 @@ if with_glx != 'disabled'
   install_headers('GL/glx.h', 'GL/glext.h', 'GL/glx_mangle.h', subdir : 'GL')
 endif
 
-if with_osmesa
+if with_osmesa != 'none'
   install_headers('GL/osmesa.h', subdir : 'GL')
 endif