Set toolchain list centrally.

Set target OS for additional operating systems: WinRT, Windows CE,
Android, FreeBSD, NetBSD, OpenBSD, BSD (generic), BlackBerry, QNX,
and Solaris.

No more "else assumptions" which would for example detect Clang on
Windows as MSVC, any non-Clang toolchains as GCC, or any unrecognized
operating systems as Unix.

bsd4 is gone as it is not necessary in any practical sense (and no other
operating systems have different identifiers by version -- there is a
dedicated hostOSVersion property anyways).

Detect iOS without relying on Qt.

Change-Id: I38e2adf188d4604182ec84003dc5d281fce025cc
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>