Simplify the log accumulation code. It turns out that the trick of

Simplify the log accumulation code.  It turns out that the trick of
looking for ^===> can give quite annoying false positives, especially
when building kernels, so drop it; the context can be inferred from
make's "Stop in /foo/bar/baz" messages anyway.

Also add a case that I'd missed the first time around (which happens
to be the common case, not the exception...)