The current IPv6 support is half-assed and breaks for too many people.
Revert back to IPv4 only for now.

execution disabled on certain source files; some comments on java binding; MSVC temp files added to .gitignore

Fixes git builds w/o asciidoc, bug introduced in 46824abe

We only care about libstdc++ when using GNU C++.
Further, libstdc++ depends on libm on some platforms, fix this.

This fixes the build_doc logic to work as advertised and never
try to (re)build documentation when working with a tarball release.

It turns out that feature test macros are a complete mess, and defining
_GNU_SOURCE and _POSIX_C_SOURCE together breaks some systems. So we try
and define the appropriate "make everything visible" combination specific
to each system instead. This may still break something, so people should
test their platforms and speak up if so.