MacOS::Version: add :tiger
sqlite 3.7.17
zeromq: apply patch for strndup on 10.6

Fixes #19877.
link: extract keg-only check into a helper method
build: use ARGV.interactive? instead of .flag?
Add test for ARGV.flag?
Simplify implementation of ARGV.flag? and .switch?
CompilerSelector: raise when no compatible compiler

This replaces the old behaviour of falling back to the original
compiler with no messaging.

Fixes #19170.
Fixes mistydemeo/tigerbrew#45.
Add gcc 4.0 to CompilerSelector compiler queue