Silent C++ runtime dependence

On Linux (but possibly Windows as well) when consuming glslang as a static library - as is the default with Vcpkg (which is how I found this bug) - in a C application, the `glslang::glslang` target silently depends on libstdc++.

If the project exports a C API, it likely wants to link the C++ runtime statically into itself when it is built as a static library. See WHOLE_ARCHIVE in the CMake docs.

Start with the glslang::glslang CMake target and the CMake documentation for WHOLE_ARCHIVE. Reproduce a static-library build consumed by a C application through Vcpkg, then verify that the exported target handles its C++ runtime dependency without requiring consumers to discover it themselves.

Written by the indexing model from the issue text.