stage2: print package path on --pkg-begin failure
stage2: print package path on --pkg-begin failure

This makes it much easier for the user to figure out what has gone wrong
than dumping an error return trace.

andrewrk/zig,raulgrell/zig,andrewrk/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,zig-lang/zig,raulgrell/zig,zig-lang/zig