While both long and long long are 64-bits on x86_64, they are distinct types,
and long was used prior to commit 477463a2011ba81907a753df9ce7a71b6563db54.
Changing this breaks the linking of previously compiled C++ functions with
off_t arguments on 64-bit Cygwin with newly compiled code, as the mangling of
long (l) and long long (x) differ.
Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>