func_realpath doesn't check errno at all.  When running in parallel builds, if the parent gmake process receives a signal in the middle of calling `realpath` it'll act as though the file does not exist.

Suggested fix:


2028c2017
<  while ( errno == EINTR || (path = find_next_token (&p, &len)) != 0)
---

>  while ( (path = find_next_token (&p, &len)) != 0)

The above use of || will shortcut and prevent it from pre-maturely grabbing the next token.

I haven't evaluated this to see if something more comprehensive could/should be done (eg, checking other "errno" values, etc).

I haven't finished validating whether this completely resolves the problem, but so far it seems to have done just that.  Furthermore, I don't have any ideas for how to implement a test for this as it's a race condition that isn't necessarily easy to reproduce.

I highly recommend evaluating other system functions used by gmake to determine whether this sort of issue could crop up elsewhere (eg, `$(abspath ...)`, etc)