MFH: r531689

emulators/virtualbox-ose: Switch build to USES= compiler:c++14-lang

The runtime breakage that started occurring after the LLVM 7 -> 8 transition
has been diagnosed with help from cem@, and the attached patch fixes it. The
problem ended up being that tail-call optimization was being applied to this
function (which should probably be written in assembly instead) and moving
the tail-call to later on after some stack manipulations. The problem with
this is that this particular function uses alloca() to carefully craft a
stack that it's expecting to be used for the function it's calling at the
end.

The new patch fixes this using a technique that was committed later on in
upstream changeset 75061 to address a similar failure with GCC sanitizers
enabled. The FreeBSD-specific component of this patch is using the different
stack setup if clang is defined as well.

The extra hunk in the Config patch has been added because the VirtualBox
build system cannot cope with LLVM version numbers in the way it's
expecting. Hardcode it to GCC 4.2 for FreeBSD, which is what the clang
__GNU* macros describe, to fix build breakage that happens with newer LLVM
as the build system decides our LLVM is an even older and more broken
version of GCC with a broken regparm.

PR: 236616, 244847
Approved by: koobs (mentor)

Approved by: ports-secteam (blanket: major runtime fix caused by bad build)