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