When targeting a platform that supports multiple architectures, Xcode
may choose to build all of them in our small compiler id project.
Update the regex we use to extract the path to the compiler from
the Xcode output to account for this.

Fixes: #21425

Capture CMAKE_<LANG>_COMPILER_ARG1 from CMAKE_<LANG>_COMPILER in the
same fashion that it is from $ENV{<LANG>}.

Since get_filename_component() returns a single string of all the
arguments from $ENV{<LANG>}, a single string of arguments will be
constructed from the items contained in CMAKE_<LANG>_COMPILER.

Fixes #20089

If the `OBJC` or `OBJCXX` environment variable is not set to specify an
Objective C or C++ compiler, check `CC` or `CXX` too.

Fixes: #20703

Now detect _CMAKE_TOOLCHAIN_PREFIX whenever a compilers
name matches the heuristics, instead of only doing it
when cross compiling

Steve Wilson authored 5 years ago and Cristian Adam committed 5 years ago

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 OBJCXX as the designator of the language, eg:

project(foo OBJCXX)

Add various tests for Objective-C++ language features.  Add
tests to preserve C++ handling of .M and .mm files when
Objective-C++ is not a configured language.

Co-authored-by: Cristian Adam <cristian.adam@gmail.com>