More nuanced debug info choice

[jrose-signal]

Today, cc checks whether DEBUG is set, and if so directs the underlying compiler to produce debug info. However, DEBUG is not just a binary option; it's the "[value] of the corresponding [variable] for the profile currently being built", which in turn may be one of several options. I know this won't ever be perfect, but it would be great if e.g. setting debug = "line-tables-only" actually translated into passing -gline-tables-only when using Clang and -g1 when using GCC (and some nearby thing on MSVC). Or at least some more constrained upper bound than "full debug info".

[NobodyXu]

Yeah that's much better than what we have now, I will accept a PR for this.