Environment: clear everything and have known settings
Two reasons for this. First, having a predicable environment ensures that test machines, prod machines, etc all have a known environment for building that removes some sources of entropy.
Perhaps more important, this would be a significant speed win on (at least) Power. A typical user session environment (with things like LS_COLORS, DBus properties, etc) can add between 3-5ms per executable invocation on Power due to pessimistic copying of envp
crossing user/kernel boundaries. We saw a 4x speedup on just configure
runs having a minimal environment during RC1/RC2 builds. Across the entire package tree, there are significant gains to be had - especially in situations like system/libtool
's test suite.