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: I9ffc49cb6ba05551b593c2a312ca267f52c9b9c9
Signed-off-by: Thang Q. Nguyen <thang@os.amperecomputing.com>
diff --git a/meson_options.txt b/meson.options
similarity index 100%
rename from meson_options.txt
rename to meson.options