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drm/amdgpu: fix stack alignment ABI mismatch for Clang
The x86 kernel is compiled with an 8B stack alignment via `-mpreferred-stack-boundary=3` for GCC since 3.6-rc1 via commit d9b0cde9 ("x86-64, gcc: Use -mpreferred-stack-boundary=3 if supported") or `-mstack-alignment=8` for Clang. Parts of the AMDGPU driver are compiled with 16B stack alignment. Generally, the stack alignment is part of the ABI. Linking together two different translation units with differing stack alignment is dangerous, particularly when the translation unit with the smaller stack alignment makes calls into the translation unit with the larger stack alignment. While 8B aligned stacks are sometimes also 16B aligned, they are not always. Multiple users have reported General Protection Faults (GPF) when using the AMDGPU driver compiled with Clang. Clang is placing objects in stack slots assuming the stack is 16B aligned, and selecting instructions that require 16B aligned memory operands. At runtime, syscall handlers with 8B aligned stack call into code that assumes 16B stack alignment. When the stack is a multiple of 8B but not 16B, these instructions result in a GPF. Remove the code that added compatibility between the differing compiler flags, as it will result in runtime GPFs when built with Clang. Cleanups for GCC will be sent in later patches in the series. Link: https://github.com/ClangBuiltLinux/linux/issues/735 Debugged-by:Yuxuan Shui <yshuiv7@gmail.com> Reported-by: