winex11.drv compile failure

[James Hawkins]

Compile fails for me with today's git:

opengl.c: In function 'ConvertAttribWGLtoGLX':
opengl.c:676: error: 'GLX_RGBA_FLOAT_BIT_ARB' undeclared (first use in
this function)
opengl.c:676: error: (Each undeclared identifier is reported only once
opengl.c:676: error: for each function it appears in.)
opengl.c: In function 'get_render_type_from_fbconfig':
opengl.c:845: error: 'GLX_RGBA_FLOAT_BIT_ARB' undeclared (first use in
this function)
opengl.c:846: error: 'GLX_RGBA_FLOAT_TYPE_ARB' undeclared (first use
in this function)