Update the logic that converts a `try_compile` result from a cache
entry to a normal variable to tolerate an existing normal variable
under CMP0126 NEW behavior. Otherwise the `try_compile` result
is ignored because CMake uses the false value of the normal variable,
and CMake incorrectly reports that the compiler does not work.
This went unnoticed for some languages (e.g. C and CXX) because the
check for a working compiler is skipped if ABI detection works.
It does affect other languages (e.g. CSharp).
Fixes: #22423
We run a `try_compile` with a tiny test source to check if the compiler
works so that we can fail early if it does not. When the compiler does
work, we immediately `try_compile` the ABI detection source. In the
common case that both steps work, we gain no useful information from the
first one and the work was wasted.
Re-order the checks to try the ABI detection first. If it works then
assume the compiler works and skip the dedicated check. If the ABI
check fails then proceed with the normal test for a working compiler so
the diagnostic can be shown as before.
Fixes: #18703
Add entries in Modules and Modules/Platform to support
Objective-C compiler determination and identification.
Add Modules to check Objective-C compiler flags, source
compilations, program checks, etc...
Use OBJC as the designator of the language, eg:
project(foo OBJC)
Add various tests for Objective-C language features. Add
tests to preserve C++ handling of .m and .mm files when
OBJC is not a configured language.
Co-Authored-By: Cristian Adam <cristian.adam@gmail.com>
