meson_options.txt: Support for reading options from meson.options

Support has been added for reading options from meson.options instead
of meson_options.txt[1]. These are equivalent, but not using the .txt
extension for a build file has a few advantages, chief among them
many tools and text editors expect a file with the .txt extension to
be plain text files, not build scripts.

[1] https://mesonbuild.com/Release-notes-for-1-1-0.html#support-for-reading-options-from-mesonoptions

Change-Id: I5f018fbf230cea3a593a87cad83822e944bfaaf2
Signed-off-by: George Liu <liuxiwei@inspur.com>
diff --git a/meson_options.txt b/meson.options
similarity index 100%
rename from meson_options.txt
rename to meson.options