Continues #51093 .

Background: on macOS, parallel builds of postgres would try to build libpgtypes.a multiple times, trip over each other and error out.

On the postgres mailing list, Tom Lane figured out that:

• APFS has sub-second timestamp resolution
• GNU Make can use sub-second timestamps if the filesystem supports them
• ranlib truncates timestamps to the nearest second
  • Thomas Munro identifies a possible cause
• Therefore, the .a file appears to be built before the .o files that comprise it
• Therefore, multiple builds of libpgtypes.a are kicked off, trip over each other and error out.

GNU Make has a special target, .LOW_RESOLUTION_TIME, that can be used in this situation.

I won't have time to dig much further on this, but thought I'd log the issue for completeness. Ping @delroth , who wasn't thrilled at the blunt hammer of disabling parallel builds.