OK. We don't really need a bsd.stand.mk, and it was causing a -fPIC
for the toolchain to be added (bogusly) when building on amd64. Pull
all relevant defs back into defs.mk and delete bsd.stand.mk.
This saves about 15-20k on i386 loader and zfsloader which when
combined with Lua give us a lot more stack space in those constrained
environments.
MK_CTF, MK_SSP, MK_PROFILE, NO_PIC, and INTERNALLIB are always the
same, so set them in defs.mk. MAN= is common, so set it here too.
This removes a lot of boring repetition from the Makefiles that added
almost no value.
Default WARNS to 0 still, since there's still some warnings on other
architectures.
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D13301
