K 10
svn:author
V 6
rlibby
K 8
svn:date
V 27
2019-11-29T06:25:07.832477Z
K 7
svn:log
V 664
kern.mk: -Wno-error=stringop-overflow for gcc due to false positives

Demote gcc's Wstringop-overflow to Wno-error due to false positives.
E.g. the riscv64 build with gcc 8.3.0 has been failing with this warning
since r355062 [1].  A bug has been filed with gcc [2].  The warning was
first introduced in gcc 7.1 [3]. Hopefully we can avoiding suppressing
the warning in future gcc versions.

[1] https://ci.freebsd.org/job/FreeBSD-head-riscv64-build/16691/
[2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92718
[3] https://gcc.gnu.org/wiki/WarningHistory

Reviewed by:	markj
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D22603

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