Fix locking bugs that could corrupt pg_control.

Fix locking bugs that could corrupt pg_control.

The redo routines for XLOG_CHECKPOINT_{ONLINE,SHUTDOWN} must acquire
ControlFileLock before modifying ControlFile->checkPointCopy, or the
checkpointer could write out a control file with a bad checksum.

Likewise, XLogReportParameters() must acquire ControlFileLock before
modifying ControlFile and calling UpdateControlFile().

Back-patch to all supported releases.

Author: Nathan Bossart <[email protected]>
Author: Fujii Masao <[email protected]>
Reviewed-by: Fujii Masao <[email protected]>
Reviewed-by: Michael Paquier <[email protected]>
Reviewed-by: Thomas Munro <[email protected]>
Discussion: https://postgr.es/m/70BF24D6-DC51-443F-B55A-95735803842A%40amazon.com