Fix finding wayland-client.h on Linux

[rhabacker]

When compiling with the wayland-client package on Linux, the corresponding headers are installed in a subdirectory of /usr/include. This path is not added to the compiler search path by openxr, so the required file 'wayland-client.h' is not found.

In file included from /home/user/src/vsgFramework-build/components/vsgvr-src/deps/openxr/src/common/platform_utils.hpp:12:0,
                 from /home/user/src/vsgFramework-build/components/vsgvr-src/deps/openxr/src/common/filesystem_utils.cpp:13:
/home/user/src/vsgFramework-build/components/vsgvr-src/deps/openxr/src/common/xr_dependencies.h:88:10: fatal error: wayland-client.h: file not found
 #include "wayland-client.h"
          ^~~~~~~~~~~~~~~~~~

To fix the problem, the include directories provided by the pkgconfig module for wayland-client are added to the corresponding cmake targets.

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[rhabacker]

superseeded by https://github.com/KhronosGroup/OpenXR-SDK-Source/pull/346