Revert "[cfi-icall] Refactor GL g_driver_* to be CFI-safe"

This reverts commit a71b54d8.

Reason for revert: Breaking the Linux Debug NVidia bot. See crbug.com/795332 for more details.

Original change's description:
> [cfi-icall] Refactor GL g_driver_* to be CFI-safe
> 
> Control Flow Integrity [1] indirect call (cfi-icall) checking can not
> verify that dynamically resolved function pointers call their intended
> function. To account for this, we place the function pointers in the
> various g_driver_* structs in ProtectedMemory, a wrapper for keeping
> variables in read-only memory except for when they are initialized.
> Once they are set they can not be tampered with since the memory is set
> back to read-only.
> 
> The generated bindings in gl_bindings_autogen_*.cc are not aware of the
> fact that their implementation is held in protected memory, so instead
> of using base::UnsanitizedCfiCall() we mark the individual function
> stubs with __attribute__((no_sanitize("cfi-icall"))) to disable icall
> checks on the generated bindings since their function pointer calls
> are routed through protected memory.
> 
> [1] https://www.chromium.org/developers/testing/control-flow-integrity
> 
> Bug: 771365
> Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
> Change-Id: I6bbf1b9a4122e1d00f6d2a365ae3730b4bb95a73
> Reviewed-on: https://chromium-review.googlesource.com/770252


> Commit-Queue: Peter Collingbourne <pcc@chromium.org>
> Reviewed-by: Dan Sanders <sandersd@chromium.org>
> Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
> Reviewed-by: Peter Collingbourne <pcc@chromium.org>
> Reviewed-by: Daniel Cheng <dcheng@chromium.org>
> Reviewed-by: Kenneth Russell <kbr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#524318}

TBR=dcheng@chromium.org,dalecurtis@chromium.org,kbr@chromium.org,sandersd@chromium.org,pcc@chromium.org,vtsyrklevich@chromium.org

Change-Id: Ib4a1eae5e9f01f5e9ddbb1fcc5c66fc0b91f1015
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 771365, 795332
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Reviewed-on: https://chromium-review.googlesource.com/830173


Reviewed-by: Eric Karl <ericrk@chromium.org>
Commit-Queue: Eric Karl <ericrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524411}