Help: Document OBJC and OBJCXX env vars for Objective C/C++ compilers

Help/envvar/OBJC.rst

@@ -0,0 +1,11 @@
+OBJC
+----
+
+.. include:: ENV_VAR.txt
+
+Preferred executable for compiling ``OBJC`` language files. Will only be used
+by CMake on the first configuration to determine ``OBJC`` compiler, after
+which the value for ``OBJC`` is stored in the cache as
+:variable:`CMAKE_OBJC_COMPILER <CMAKE_<LANG>_COMPILER>`. For any configuration
+run (including the first), the environment variable will be ignored if the
+:variable:`CMAKE_OBJC_COMPILER <CMAKE_<LANG>_COMPILER>` variable is defined.

Help/envvar/OBJCXX.rst

@@ -0,0 +1,11 @@
+OBJCXX
+------
+
+.. include:: ENV_VAR.txt
+
+Preferred executable for compiling ``OBJCXX`` language files. Will only be used
+by CMake on the first configuration to determine ``OBJCXX`` compiler, after
+which the value for ``OBJCXX`` is stored in the cache as
+:variable:`CMAKE_OBJCXX_COMPILER <CMAKE_<LANG>_COMPILER>`. For any configuration
+run (including the first), the environment variable will be ignored if the
+:variable:`CMAKE_OBJCXX_COMPILER <CMAKE_<LANG>_COMPILER>` variable is defined.

Help/manual/cmake-env-variables.7.rst

@@ -54,6 +54,8 @@ Environment Variables for Languages
    /envvar/CXXFLAGS
    /envvar/FC
    /envvar/FFLAGS
+   /envvar/OBJC
+   /envvar/OBJCXX
    /envvar/RC
    /envvar/RCFLAGS
    /envvar/SWIFTC