Disable warn-error, as it makes developing on a trunk compiler very difficult
Merge pull request #1367 from avsm/no-warn-error

Disable warn-error, as it makes developing on a trunk compiler hard
Remove -warn-error in the Makefile version too.

Followup to 1e2b8cc677942ba56301781107dcf841f0d849a7 which removed
them for ocp-build
Merge pull request #1368 from avsm/fix-warn-error3

Remove -warn-error in the Makefile version too.
Makefile: fix dependencies calculation