[coreboot-gerrit] Change in coreboot[master]: Treewide: Add some gcc's warning options

[Martin Roth (Code Review)]

Martin Roth has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/39406 )

Change subject: Treewide: Add some gcc's warning options
......................................................................

Patch Set 2: Code-Review+2

Tested with scanbuild as well.  No issues there.

We might want a way to disable the warnings for local builds, maybe tied to the "use any toolchain" option.  Or not.  I'm just not sure what versions of GCC people use if they're not using the coreboot toolchain, and I don't know what version of GCC these warnings were added.