Since commit 3f2a5971c0 (Modules: CMAKE_*_COMPILER convert path to cmake
path, 2023-12-02, v3.29.0-rc1~292^2) we normalize the path to the
compiler. Update our logic that checks whether the compiler has changed
to account for path normalization.
Fixes: #25883
Issue: #25456
Since commit 7d47c693 (Drop compatibility with CMake < 2.4, 2013-10-08)
we no longer need to use the configure_file IMMEDIATE option to support
compatibility modes less than 2.0.
Add RunCMake.CompilerChange test to cover use of -DCMAKE_C_COMPILER=cc
to change the compiler of an existing build tree. Also test for proper
failure with -DCMAKE_C_COMPILER="" and no CC in the environment.
