Clean up and fix fseek64/ftell64
Test for the exception systems, GNU and Windows, and then fall back to standard POSIX.
This fixes build with musl libc, which does not have fseeko64/ftello64.
Fixes #1241 (closed)
Test for the exception systems, GNU and Windows, and then fall back to standard POSIX.
This fixes build with musl libc, which does not have fseeko64/ftello64.
Fixes #1241 (closed)