Introduce new headers whose inclusion forces linking and

Introduce new headers whose inclusion forces linking and
initialization of all targets (InitializeAllTargets.h) or assembler
printers (InitializeAllAsmPrinters.h). This is a step toward the
elimination of relinked object files, so that we can build normal
archives.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73543 91177308-0d34-0410-b5e6-96231b3b80d8