time_rz.c and Android NDK r27

[Po Lu]

This new release of the Android NDK defines timezone_t in time.h whether
or not it defines the related tzalloc and localtime_rz extensions, which
being new APIs are controlled by __ANDROID_API__ as expected.
Consequently, when building for earlier Android releases with this NDK,
Emacs compilation reports:

  CC       nproc.o
  CC       nstrftime.o
In file included from nstrftime.c:19:
./strftime.c:1900:17: error: call to undeclared function 'mktime_z'; ISO C99 
and later do not support implicit function declarations 
[-Wimplicit-function-declaration]
 1900 |             t = mktime_z (tz, &ltm);
      |                 ^
./strftime.c:1900:17: note: did you mean 'mktime'?
/opt/android/android-ndk-r27/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/time.h:159:8:
 note: 'mktime' declared here
  159 | time_t mktime(struct tm* _Nonnull __tm);
      |        ^
1 error generated.