meson: fix build for egl platform_x11 without dri3 and gbm
Compiling EGL's platform_x11 without dri3 and gbm yields this compile failure: platform_x11 needs inc_loader: ../mesa-18.2.0-rc2/src/egl/drivers/dri2/platform_x11.c:48:10: fatal error: loader.h: No such file or directory #include "loader.h" ^~~~~~~~~~ Fixes: 108d257a ("meson: build libEGL") Bugzilla: https://bugs.gentoo.org/663534 Reviewed-by:Matt Turner <mattst88@gmail.com>