I'm quite fond of doing VPATH builds, i.e. building outside the source

I'm quite fond of doing VPATH builds, i.e. building outside the source
tree. This also catches lots of little Makefile bugs, so here's a small
patch for one of them (replacing an explicit reference to thread.c with
a reference to it as the first prerequsite of the rule makes make look
for it in the place where it was found (the source tree) rather than in
the build tree. (using GNU make 3.79.1)

John Gray