musl 1.2.4 deprecated legacy "LFS64" ("large file support") interfaces so
just having _GNU_SOURCE defined is not enough anymore.
_LARGEFILE64_SOURCE has to be defined in the source, or CFLAGS can be used
to pass -D_LARGEFILE64_SOURCE to allow to keep using LFS64 definitions.
Signed-off-by: Robert Marko <robimarko@gmail.com>