Add usr.bin/clang/clang and change NO_LLVM_TOOLS

After checking FreeBSD, it appears llvm tools aren't on the base
system.  I verified with share/mk/bsd.opts.mk that it's not normally
built.  Switch the defaults and switch the label to LLVM_TOOLS instead
of NO_LLVM_TOOLS.
Augment objformat and remove mips, sparc, powerpc from clang