The linker configuration file is now optional: It is loaded only if
variable CMAKE_<LANG>_USE_LINKER_CONFIGURATION is set to TRUE.
The file CMakeAddNewLanguage.txt is updated to take into account the
linker configuration.
Fixes: #26393
The `Platform/<OS>.cmake` modules record platform-specific flag
variables for the C toolchain. The `CMake<LANG>Information` modules
initialize the per-language platform-specific flag variables to defaults
copied from C. However, they have diverged over time, and not all
platform-specific flag variables are initialized correctly for all
languages. Factor out the CXX language's instance of this logic into a
helper macro, and reuse it for all languages for which we previously
had the platform-specific flag variables at least partially filled out.
Previously the Fortran language's copy of this logic used
`if(NOT DEFINED <var>)` instead of just `if(NOT <var>)` to allow
`Platform/<OS>-<COMPILER_ID>-<LANG>` modules to specify empty values for
some platform-specific flag variables without being overridden.
Use this approach in the helper macro so it applies to all languages.
Fixes: #25990
Currently, this feature is only supported on ELF platforms. So, the property
LINK_WHAT_YOU_USE will be ignored for other plateforms.
Moreover, flags and commands are now controled by CMake variables.
Fixes: #20174
In commit 8d61294c3e (PCH: Mark CMake PCH source files as -x
<lang>-header, 2020-09-04, v3.18.3~14^2) we removed the explicit `-x
objective-c++` flag. This broke cases with custom source extensions.
Restore the explicit `-x objective-c[++]` flag and put it before the
`<FLAGS>` placeholder. The latter will contain the proper `-x
objective-c[++]-header` value and will override the `-x objective-c[++]`
value set before.
Fixes: #21234
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>
