32-bit android uses 32-bit off_t by default. When building with
-D_FILE_OFFSET_BITS=64 with unified headers off_t are promoted
to 64-bit, but there are bugs in the toolchain and spotty support
for it in the platform (not all functions are available until
android-24, and the platform zlib is compiled with 32-bit off_t).
Also, unless every library&program is rebuilt with 64-bit off_t,
including user-built ones, we risk a mismatch between programs and
libraries which can cause serious (but sometimes subtle) runtime
failures.
As -D_FILE_OFFSET_BITS=64 is not that important for most users
(with mariadb requiring it as an exception), we drop the support
for now by patching it away in <sys/cdefs.h>.
The librt and libpthread libraries are built into libc on Android
and does not exist as separate libraries.
We now set them up as symlinks to libc for compatibility.
Fixes#403.
