libclc: Make all built-ins overloadable

The SPIR spec states that all OpenCL built-in functions should be
overloadable and mangled, to ensure consistency.

Add the overload attribute to functions which were missing them:
work dimensions, memory barriers and fences, and events.

Reviewed By: tstellar, jenatali

Differential Revision:

GitOrigin-RevId: 3d21fa56f5f5afbbf16b35b199480af71e1189a3
41 files changed