A few warnings were causing build errors on Arm 64.
Since we don't want to modify the LLVM code itself,
the warnings in the LLVM code are now suppressed.

Bug chromium:922089

Change-Id: I7e8827cda5117e8817342930dca8d7b7f90d339c
Reviewed-on: https://swiftshader-review.googlesource.com/c/23628Tested-by: Alexis Hétu <sugoi@google.com>
Tested-by: Corentin Wallez <cwallez@google.com>
Reviewed-by: Corentin Wallez <cwallez@google.com>