Android.mk: Provide a custom entry name to ensure meson checks succeed

Android.mk: Provide a custom entry name to ensure meson checks succeed

When meson tests for the compability of some linker flags, not having
the default entry symbol "_start" defined makes the check fail for
a warning unrelated to the linker flag meson is testing.

Since these tests normally just try to compile a C program with a main,
use "main" as the ficticious entry point.

Specifically, this makes "-Wl,--build-id=sha1" recognised as valid
and allows its use for drivers that rely on it.

This is a temporary workaround that is required until Android.mk is
changed to support both shared libraries and executables.

Cc: "22.0" "22.1" "22.2" mesa-stable
Reviewed-by: Roman Stratiienko <r.stratiienko@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17715>