cmake: LINKER_LANGUAGE is a target property, not a cmake variable

LINKER_LANGUAGE needs to be used as following:
Usage

  cmake [options] <path-to-source>
  cmake [options] <path-to-existing-build>
  cmake [options] -S <path-to-source> -B <path-to-build>

Specify a source directory to (re-)generate a build system for it in the
current working directory.  Specify an existing build directory to
re-generate its build system.

Run 'cmake --help' for more information.

Haiku does not not this property explicitly set because CMake knows .cc files are c++

CMakeLists.txt

@@ -11,10 +11,6 @@ else()
   set(SDL3_SUBPROJECT ON)
 endif()
 
-if (HAIKU)
-  set(LINKER_LANGUAGE CXX)
-endif()
-
 set(EXTRA_LIBS)
 set(EXTRA_LDFLAGS)