The compiler does not yet support everything needed to integrate well
with the MSVC ABI, in particular for runtime library selection and debug
format selection. Document them in FIXME comments and leave this
support undocumented by CMake for now.
Fixes: #24840
Inspired-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
LLVM Flang's preprocessor output is always valid fixed form Fortran with
a fixed line length of 72. If an application tries to use fixed form
with a different line length, this will fail in the
post-preprocessing compilation step as they will pass a flag asking for
a different fixed line length.
To fix this we can pass -ffixed-line-length-72 to the post-preprocess
compilation stage. This will be ignored when the input is free form
Fortran, and force to a 72 line length when the input is fixed.
Parse implicit link information for this compiler to support
mixed-language linking. This was missed by commit 85749766df
(LLVMFlang: Add support for LLVM Flang, 2021-07-07, v3.24.0-rc1~86^2).
Also activate mixed-language test cases that would have caught this.
Issue: #22387
LLVM Flang (https://github.com/llvm/llvm-project/tree/main/flang) is an LLVM
Fortran compiler that shares the same name as Flang (also known as Classic
Flang). Classic Flang is in active development and is already identified by
CMake as Flang. As such, LLVM Flang will be identified as `LLVMFlang`.
Fixes: #22387
