st/wgl: consistently use ifndef guards over pragma once
st/wgl: consistently use ifndef guards over pragma once

Signed-off-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>
Acked-by: Vedran Miletić <1f690334c6c53f00d3d03a274ae96d5728a3cf31@miletic.net>
Acked-by: Juha-Pekka Heikkila <cab67866509becb852d2a4e6f7e5924ad04fb975@gmail.com>
Reviewed-by: Edward O'Callaghan <b035da0d7e151e09fe2005f3a7bc526beb9b3245@folklore1984.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler