This brings in libgcov and fixes the FreeBSD LINT[0]
kernel build that includes GCOV[1].
This also requires a workaround to ensure that
ALL_TARGET is processed sequentially, because at
higher core counts, libgcc configure fails
when it can't find a prebuilt xgcc binary.
[0] https://cgit.freebsd.org/src/tree/sys/amd64/conf/NOTES?id=886164895f3f4805dc11171ac7980acaccf6ec77#n10
[1] https://cgit.freebsd.org/src/tree/sys/conf/kern.pre.mk?id=886164895f3f4805dc11171ac7980acaccf6ec77#n104