tm_zone can be const in some systems

[Hugmeir]

It appears that in glibc and QNX NTO[0], tm_zone is always const.
Meanwhile, on Android[1] tm_zone is const, but somehow loses its constness if you use C++[2].

/* If glibc is defined or we are on QNX, use const.
 * Otherwise, if we are on android, use const but
 * not with g++.
 */
#  if defined(__GLIBC__) || (defined(__ANDROID__) && !defined(__cplusplus)) || defined(__QNX__)
        const
#  endif

[0] The header is in Blackberry's NDK, but I honestly can't find a public repo -- even the link in the source code gives me a 404
[1] https://github.com/android/platform_bionic/blob/master/libc/include/time.h
[2] No clue. Found this when trying to cross-compile Perl using g++.