[llvm] Reland [llvm] Add support for llvm IR atomicrmw fminimum/fmaximum instructions (PR #137701)

[Jonathan Thackray via llvm-commits]

jthackray wrote:

@kazutakahirata How are you building? I'm using:
```
cmake \
  -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_INSTALL_PREFIX=$INSTALLDIR \
  -DCMAKE_CXX_STANDARD=17 \
  -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
  -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$LD_LIBRARY_PATH" \
  -DFLANG_ENABLE_WERROR=ON \
  -DLLVM_ENABLE_ASSERTIONS=ON \
  -DLLVM_TARGETS_TO_BUILD=host \
  -DLLVM_LIT_ARGS=-v \
  -DLLVM_ENABLE_PROJECTS="clang;mlir;flang;openmp" \
  -DLLVM_ENABLE_RUNTIMES="compiler-rt;flang-rt" \
  ../llvm-project/llvm
```
from https://flang.llvm.org/docs/GettingStarted.html and it builds fine (6913 files) for me? 🤷🏻 

https://github.com/llvm/llvm-project/pull/137701