Fix -fuse-ld to be linker flag in feature detection check

Discovered an issue working in StableHLO when attempting to build with `-Wall -Werror`:
openxla/stablehlo#137

Currently, if `LLVM_USE_LLD` and `-DCMAKE_CXX_FLAGS="${CMAKE_CXX_FLAGS} -Wall -Werror"`
are both specified for build, the build will error with:

```
-- Performing Test CXX_SUPPORTS_CUSTOM_LINKER - Failed
CMake Error at /usr/local/google/home/gleasonk/Coding/llvm-build/lib/cmake/llvm/HandleLLVMOptions.cmake:309 (message):
  Host compiler does not support '-fuse-ld=lld'
...

$ cat <build_dir>/CMakeFiles/CMakeError.log
...
clang: error: argument unused during compilation: '-fuse-ld=lld' [-Werror,-Wunused-command-line-argument]
```

It looks like other repos have hit this same issue:
- golang/go#41527 (mentioned in comment)
- iree-org/iree#7450

This can be reproduced in llvm-project with the following build command:

```
# Compile command taken from https://mlir.llvm.org/getting_started/
# and modified for use case
cmake -G Ninja ../llvm \
   -DLLVM_ENABLE_PROJECTS=mlir \
   -DLLVM_BUILD_EXAMPLES=ON \
   -DLLVM_TARGETS_TO_BUILD="X86;NVPTX;AMDGPU" \
   -DCMAKE_BUILD_TYPE=Release \
   -DLLVM_ENABLE_ASSERTIONS=ON \
   -DCMAKE_CXX_COMPILER=clang++ \
   -DCMAKE_C_COMPILER=clang \
   -DLLVM_ENABLE_LLD=ON \
   -DCMAKE_CXX_FLAGS="${CMAKE_CXX_FLAGS} -Wall -Werror"
```

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D134206

Author: GleasonK

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -302,15 +302,12 @@ if( LLVM_ENABLE_LLD )
 endif()
 
 if( LLVM_USE_LINKER )
-  set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
-  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fuse-ld=${LLVM_USE_LINKER}")
+  append("-fuse-ld=${LLVM_USE_LINKER}"
+    CMAKE_EXE_LINKER_FLAGS CMAKE_MODULE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
   check_cxx_source_compiles("int main() { return 0; }" CXX_SUPPORTS_CUSTOM_LINKER)
   if ( NOT CXX_SUPPORTS_CUSTOM_LINKER )
     message(FATAL_ERROR "Host compiler does not support '-fuse-ld=${LLVM_USE_LINKER}'")
   endif()
-  set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
-  append("-fuse-ld=${LLVM_USE_LINKER}"
-    CMAKE_EXE_LINKER_FLAGS CMAKE_MODULE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
 endif()
 
 if( LLVM_ENABLE_PIC )