`clang-cl` supports the `-imsvc` flag to tell the compiler an include
directory is intended for system paths. `icx` does not accept this
flag, even on MSVC platforms, so do not tell CMake that it exists.
Fixes: #21801
Signed-off-by: william.r.dieter <william.r.dieter@intel.com>
Using a single ID 'IntelLLVM' for the suite of Intel compilers based on
the LLVM backend. The 'IntelLLVM' ID are used for C, C++, and Fortran.
Data Parallel C++ will be handled in a separate commit.
The C and C++ definitions are based on the Clang definitions. The Intel
LLVM-based C and C++ compilers are based on the Clang front end, so
existing Clang options are more likely to be a good match than options
for the older Intel compilers.
Fortran is based on the older Fortran front end with the LLVM backend.
It has a similar interface to the older versions, though many options
are shared with the C and C++ compilers.
Fixes: #21561
Signed-off-by: William R. Dieter <william.r.dieter@intel.com>
