xmlpool: make sure we ship options.h
xmlpool: make sure we ship options.h

The header is included in ../xmlpool.h. With the latter of which used
directly in a number of places in mesa.
Note that we can also add it (alongside t_option.h) to noinst_HEADERS,
but neither solution fixes the issue that brough us here - namely:
Do not regenerate the headers, if it already exists.

Cc: "10.5" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>
Signed-off-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>
Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler