configure.in: use C99 * configure.in: ISO9899:1999 is necessary for strtoll() on FreeBSD
10, (and may be possibly other platforms).
* configure.in (NET_LUID): include also ifdef.h as a workaround of
a bug in mingw-w64 header. [ruby-core:67103] [Bug #10640]
* configure.in (NET_LUID): include winsock2.h instead of windows.h. patch by Jon Forums in [ruby-core:67125]. [Bug #10640]