glsl/standalone: Add an option to lower the precision

Adds a --lower-precision option that just sets the LowerPrecision
compiler option. That way it can be used in unit tests to test the
precision lowering pass.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3885>

src/compiler/glsl/main.cpp

@@ -46,6 +46,7 @@ const struct option compiler_opts[] = {
    { "dump-builder", no_argument, &options.dump_builder, 1 },
    { "link",     no_argument, &options.do_link,  1 },
    { "just-log", no_argument, &options.just_log, 1 },
+   { "lower-precision", no_argument, &options.lower_precision, 1 },
    { "version",  required_argument, NULL, 'v' },
    { NULL, 0, NULL, 0 }
 };