[llvm] [FrameLowering] Use MCRegister instead of Register in CalleeSavedInfo. NFC (PR #128095)

[Jan Patrick Lehr via llvm-commits]

jplehr wrote:

This appears to have broken our build of libc on GPU on this bot: https://lab.llvm.org/staging/#/builders/97
Can you please take a look?

```
/home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.build/./bin/clang++ --target=amdgcn-amd-amdhsa -DLIBC_NAMESPACE=__llvm_libc_21_0_0_git -D__LIBC_USE_FLOAT16_CONVERSION -I/home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc -isystem /home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.build/include/amdgcn-amd-amdhsa -O3 -DNDEBUG --target=amdgcn-amd-amdhsa -DLIBC_QSORT_IMPL=LIBC_QSORT_QUICK_SORT -DLIBC_ADD_NULL_CHECKS "-DLIBC_MATH=(LIBC_MATH_SKIP_ACCURATE_PASS | LIBC_MATH_SMALL_TABLES | LIBC_MATH_NO_ERRNO | LIBC_MATH_NO_EXCEPT)" -fpie -DLIBC_FULL_BUILD -nostdlibinc -ffixed-point -fno-exceptions -fno-lax-vector-conversions -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-rtti -ftrivial-auto-var-init=pattern -fno-omit-frame-pointer -Wall -Wextra -Werror -Wconversion -Wno-sign-conversion -Wdeprecated -Wno-c99-extensions -Wno-gnu-imaginary-constant -Wno-pedantic -Wimplicit-fallthrough -Wwrite-strings -Wextra-semi -Wnewline-eof -Wnonportable-system-include-path -Wstrict-prototypes -Wthread-safety -Wglobal-constructors -nogpulib -fvisibility=hidden -fconvergent-functions -flto -Wno-multi-gpu -Xclang -mcode-object-version=none -DLIBC_COPT_PUBLIC_PACKAGING -UNDEBUG -MD -MT libc/src/strings/CMakeFiles/libc.src.strings.bcopy.dir/bcopy.cpp.o -MF libc/src/strings/CMakeFiles/libc.src.strings.bcopy.dir/bcopy.cpp.o.d -o libc/src/strings/CMakeFiles/libc.src.strings.bcopy.dir/bcopy.cpp.o -c /home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc/src/strings/bcopy.cpp
In file included from /home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc/src/strings/bcopy.cpp:12:
In file included from /home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc/src/string/memory_utils/inline_memmove.h:39:
In file included from /home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc/src/string/memory_utils/generic/builtin.h:14:
In file included from /home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc/src/string/memory_utils/utils.h:15:
/home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc/src/__support/endian_internal.h:43:13: error: unknown type name 'uint8_t'
   43 | LIBC_INLINE uint8_t
      |             ^
/home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc/src/__support/endian_internal.h:44:48: error: use of undeclared identifier 'uint8_t'
   44 | Endian<__ORDER_LITTLE_ENDIAN__>::to_big_endian<uint8_t>(uint8_t v) {
      |
```

https://github.com/llvm/llvm-project/pull/128095