Add ROCMClang as an LLVM compiler to cmake (#2184)

* Add ROCMClang as an LLVM compiler to cmake

Since CMake >= 3.21, ROCm is identified as ROCMClang.

* HIP: Fix legacy CI / hipcc

Until we get ROCM 4.4, we need to work around this new detection:
https://gitlab.kitware.com/cmake/cmake/-/blob/v3.21.0/Modules/CMakeDetermineCompilerId.cmake#L153-159

Co-authored-by: Axel Huebl <axel.huebl@plasma.ninja>

.github/workflows/hip.yml

@@ -55,6 +55,9 @@ jobs:
             -DAMReX_AMD_ARCH=gfx908                       \
             -DCMAKE_C_COMPILER=$(which clang)             \
             -DCMAKE_CXX_COMPILER=$(which hipcc)           \
+            -DCMAKE_CXX_COMPILER_ID="Clang"               \
+            -DCMAKE_CXX_COMPILER_VERSION=12.0             \
+            -DCMAKE_CXX_STANDARD_COMPUTED_DEFAULT="17"    \
             -DCMAKE_Fortran_COMPILER=$(which gfortran)    \
             -DCMAKE_CXX_STANDARD=17
         cmake --build build_full_legacywrapper -j 2

Tools/CMake/AMReXGenerateConfigHeader.cmake

@@ -43,6 +43,7 @@ function ( generate_config_header )
            set(COMPILER_ID_MACRO  __PGI)
        elseif ( ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" )       OR
                 ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "AppleClang" )  OR
+                ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "ROCMClang" )   OR
                 ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "IntelLLVM" )   )
            set(COMPILER_ID_MACRO  __llvm__)
        elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC" )