`btowc' deprecated in Android NDK r30

Building Emacs with the latest prerelease of r30 of the Android NDK,
with an __ANDROID_API__ of 36, yields the following warning in Gnulib:

In file included from regex.c:72:
./regcomp.c:892:16: warning: 'btowc' is deprecated: ASCII-only; use mbtowc() instead [-Wdeprecated-declarations]
  892 |                 wint_t wch = __btowc (ch);
      |                              ^
./regex_internal.h:150:19: note: expanded from macro '__btowc'
  150 | #  define __btowc btowc
      |                   ^
/home/[...]/android-ndk-r30-beta1/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/wchar.h:182:39: note: 'btowc' has been explicitly marked deprecated here
  182 | wint_t btowc(int __ch) __attribute__((__deprecated__("ASCII-only; use mbtowc() instead")));
      |                                       ^
In file included from regex.c:72:
./regcomp.c:2661:32: warning: 'btowc' is deprecated: ASCII-only; use mbtowc() instead [-Wdeprecated-declarations]
 2661 |   return dfa->mb_cur_max > 1 ? __btowc (b) : b;
      |                                ^
./regex_internal.h:150:19: note: expanded from macro '__btowc'
  150 | #  define __btowc btowc
      |                   ^
/home/[...]/android-ndk-r30-beta1/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/wchar.h:182:39: note: 'btowc' has been explicitly marked deprecated here
  182 | wint_t btowc(int __ch) __attribute__((__deprecated__("ASCII-only; use mbtowc() instead")));
      |                                       ^
2 warnings generated.

I think some measures should be taken to suppress or address this
warning.