Vulkan: Disable global merge for volk
Vulkan: Disable global merge for volk

This optimization pass breaks the build by exporting volk's internal
binding symbols from libGLESv2.so. Since the test binary also links volk,
this causes a SEGV as the wrong (uninitialized) function pointer is
called.

This is an LLVM bug and will be fixed upstream:
https://reviews.llvm.org/D73235

Bug: angleproject:4351
Change-Id: Iebe0eabd975f8109231df30eef8c9074af8190e9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2023910
Reviewed-by: Shahbaz Youssefi <582eeec4f08a2ccd61e3ef52115e6e7c571582de@chromium.org>
Commit-Queue: Michael Spang <e1fb1a05abba8fb04acbcbe6d766da7764320db0@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle