[Development] GL headers in Qt5GuiConfigExtras.cmake

[Peter Kuemmel]

I build 5.2.1 for a embedded system and the generated Qt5GuiConfigExtras.cmake 
fails to find GLES2/gl2.h.

The reason is that the including dir GLES2 is used twice in the find command,
"GLES2/gl2.h" is searched for in "/usr/include/GLES2", but there is no
"/usr/include/GLES2/GLES2/gl2.h":

set(_GL_INCDIRS "/usr/include/GLES2")
find_path(_qt5gui_OPENGL_INCLUDE_DIR GLES2/gl2.h
    PATHS ${_GL_INCDIRS}
    NO_DEFAULT_PATH
)

gui.pro adds GLES2 to the header path: CMAKE_GL_HEADER_NAME = GLES2/gl2.h

Should I create a patch or is this error only caused by my somehow broken setup?

Peter