On aarch64, clang interprets the compile option -mgeneral-regs-only
as disabling all FPU-related registers and instructions, which not
only include those generated by the compiler (which is how gcc would
interpret this option), but also those in (inline) assemblies written
explicitly by the programmer, which gcc does not forbid with this
option. This commit enables FPU-related registers and instruction
explicitly in the FPU-context switching code, so the kernel will build
under clang-18 on aarch64. The commit that changed the behaviour
between clang-17 and clang-18 is eabffc7 of the LLVM project.
Signed-off-by: Liu, Chang <cl91tp@gmail.com>
edde814ceb