fragile pre-freeze packages

[nia <nia%NetBSD.org@localhost>]

some proposals

llvm/clang
	all major versions are backwards incompatible
	new major versions are frequent

	we should ideally always version these for zig, rust,
	include-what-you-use, etc etc, but, for now,

	updates should be held back on prior to a freeze so
	we can be sure of no bulk build fallout


firefox (non-esr), rust
	can come with surprising new platform requirements, should
	be held back on unless you can test that it works properly
	and is stable on all platforms where people commonly use
	pkgsrcfox.

qt5, boost, poppler, rust
	often these have small API breakages on minor releases, and
	can cause a surprising amount of fallout.

	it makes sense to hold back on updates prior to a freeze UNLESS
	you can run a full bulk build on your private tree and fix any
	fallout before committing.

gmake
	will require a full bulk build with all problems fixed
	regardless of freeze status.