Source debugging in GDB.

[Ori Bernstein <ori@xxxxxxxxxxxxxx>]

Myrddin now emits .file and .loc directives when compiling for posixy
targets. This should allow stepping through Myrddin code in GDB,
setting breakpoints on lines, and other similar things, without
reading the assembly and reverse engineering what's going on.

Unfortunately, there's no similarly easy way of emitting dwarf
type info, so that's going to take a lot more work. For now,
print() is still your best bet there.
-- 
    Ori Bernstein