compiler/glsl: handle case where we have multiple users for types
Both Vulkan and OpenGL migth be using glsl_types simultaneously. Patch adds a one time init to track number of users and will release types only when last user calls _mesa_glsl_release_types.
This change fixes glsl_type memory leaks we have with anv driver.
Signed-off-by: Tapani Pälli firstname.lastname@example.org