mingw: Use ftelli64() with ftruncate()
mingw: Use ftelli64() with ftruncate()

From "Coverity 207855: Allow for ftell returning -ve numbers" (commit
c2e33f5a4d08ba15a23b15468416f54f484417ce), upstream is using the 64bit
versions of ftell() in fz_truncate_output() (implemented in
file_trincate()).

Mingw-w64's toolchain can use either MSVC's ftelli64(), or POSIX's
ftello(), with either MSVC's _chsize_s(), or POSIX's ftruncate().

MinGW.org's toolchain doesn't provide MSVC's _chsize_s() (as mentioned
in "mingw: Use ftruncate() instead of _chsize_s()", commit
2c12461c80383b6b22a7d4f3f60888cd85624a56), on the one hand, nor POSIX's
ftello() (which prompted using ftello64() in "Use fseeko64/ftello64 for
MinGW targets", commit 61f5a397563ae023622322f6c00c6fbdb017799e), on the
other.

To support MinGW.org's toolchain, a third option is provided for MinGW
targets, that uses ftelli64() with ftruncate().

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