netty#16019)

…016)

**Note**: more details are provided in the single commit messages.

## Motivation:
the epoll native transport currently fails to compile on Android, due to
a couple of compilation failures
```
transport-native-unix-common/src/main/c/netty_unix_errors.c:47:15: error: incompatible integer to pointer conversion initializing 'char *' with an expression of type 'int' [-Wint-conversion]
   47 |         char* tmp = strerror_r(errnum, strerrbuf, buflen);
      |               ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
and
```
transport-native-unix-common/src/main/c/netty_unix_socket.c:449:9: error: call to undeclared library function 'bzero' with type 'void (void *, unsigned long)'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
  449 |         bzero(&addr, sizeof(addr)); // Zap addr so we can strlen(addr.sun_path) later. See unix(4).
      |         ^
transport-native-unix-common/src/main/c/netty_unix_socket.c:449:9: note: include the header <strings.h> or explicitly provide a declaration for 'bzero'
```
- `netty_unix_socket.c` uses `bzero` (in a single place). `bzero` is
defined in `strings.h`, which however does not seem to be pulled in by
default in Android with the current includes.
Moreover, `bzero` is deprecated and was dropped in POSIX 2018. See
[POSIX 2018

docs](https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap03.html)
and [relevant AOSP 16

code](https://cs.android.com/android/platform/superproject/+/android16-release:bionic/libc/include/strings.h;l=69).
- `netty_unix_errors.c` currently uses the GNU `strerror_r` on Android.
Android, however, only exposes the GNU `strerror_r` when `_GNU_SOURCE`
is defined and only on API level 23+.
See [relevant AOSP 16

code](https://cs.android.com/android/platform/superproject/+/android16-release:bionic/libc/include/string.h;l=145?q=string.h)

## Modification:
- a [dedicated
repository](https://github.com/faenil/NettyEpollAndroidBuildFailureTest)
was spun up to allow reproducing the build failures
- it is an Android project containing the necessary plumbing to build
the epoll native transport
- it can be easily built by following the instructions in the `README`
in the project repo
- replace the deprecated `bzero` with `memset`, already used for the
very same purpose in many places in the same file.
- use the XSI `strerror_r` on Android, when `_GNU_SOURCE` is not defined

## Result:
- epoll native transport builds and `Epoll.ensureAvailability()`
succeeds on Android.
Tested on Android 16 emulator image `BP41.250916.009.A1` (x86_64), NDK
`27.0.12077973`

Co-authored-by: faenil <faenil@users.noreply.github.com>