Pedantically rename all Tool subclasses to be nouns, not verbs. NFC

Classes in Tools.h inherit ultimately from Tool, which is a noun,
but subclasses of Tool were named for their operation, such as "Compile",
wherein the constructor call "Compile(args...)" could be misconstrued
as actually causing a compile to happen.

Likewise various other methods were not harmonious with their effect,
in that "BuildLinker()" returned a "new namespace::Link(...)"
instead of a "new namespace::Linker(...)" which it now does.

Exceptions: Clang and ClangAs are un-renamed. Those are their rightful names.
And there is no particulary great way to name the "Lipo-er" and a few others.

Differential Revision: http://reviews.llvm.org/D10595

llvm-svn: 240455