Enable compilation of libdevice for AMD by adding AMDGCN to macro
guarded code parts in libdevice for enabling e.g. standard library
math function.

Add compilation workflow to SYCLLibdevice.cmake for AMD.

Follow the compilation mechanism for NVPTX
(3668c0a)
and create a single bitcode library file.

Do not select builtin LLVM intrinsics for AMDGCN by default to ensure
that stdlib functions can be found when linking against libdevice.

Ensure that the clang tests check for the correctness of the new
clang driver actions and check if the driver still links the device
code against the itt device libraries when device library linkage has
been excluded.

Fix a compilation error of Intel math function libraries for MSVC
when targeting AMD. Include "device.h" before including "device_imf.hpp"
to avoid the inclusion of <type_traits>, which failed with a
redefinition of symbols error.

Check if device lib flags get treated correctly for AMDGCN and
that the linking actions for the correct device libraries are generated.