SKIP_PRECOMPILE_HEADERS

Is this source file skipped by PRECOMPILE_HEADERS feature.

This property helps with build problems that one would run into when using the PRECOMPILE_HEADERS feature.

One example would be the usage of Objective-C (*.m) files, and Objective-C++ (*.mm) files, which lead to compilation failure because they are treated (in case of Ninja / Makefile generator) as C, and CXX respectively. The precompile headers are not compatible between languages.