Update to the 20190113 snapshot of GCC 9.

Merge r479405 | mat | 2018-09-10 from lang/gcc8-devel to lang/gcc9-devel
as well: [1]

After an include, PLIST_SUB must be appended to, not overwritten.

If it is overwritten, many values will be clobbered, and
pain will ensue.

PR: 230864 [1]
Reviewed by: mat [1]