mapi: Export all GLES 3.1 functions in libGLESv2.so

mapi: Export all GLES 3.1 functions in libGLESv2.so

Khronos recommends that the GLES 3.1 library also be called libGLESv2.
It also requires that functions be statically linkable from that
library.

NOTE: Mesa has supported the EGL_KHR_get_all_proc_addresses extension
since at least Mesa 10.5, so applications targeting Linux should use
eglGetProcAddress to avoid problems running binaries on systems with
older, non-GLES 3.1 libGLESv2 libraries.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Cc: "11.2 12.0" <mesa-stable@lists.freedesktop.org>
Cc: Mike Gorchak <mike.gorchak.qnx@gmail.com>
Reported-by: Mike Gorchak <mike.gorchak.qnx@gmail.com>
Acked-by: Chad Versace <chad.versace@intel.com>