Now that popen and pclose don't throw thousands of warnings when compiling mingw builds, some other warnings stand out.
parallel.c: In function 'pgpipe':
parallel.c:1332:2: warning: overflow in implicit constant conversion [-Woverflow]
parallel.c:1386:3: warning: overflow in implicit constant conversion [-Woverflow]
I think the solution is to use the pgsocket typedef from src/include/port.h, rather than int. Like attached.
But I'm far from being a typedef lawyer, so maybe I am all wet.
Cheers,
Jeff