Remove the Tools DensMap from the toolchain.

Remove the Tools DensMap from the toolchain.

Each toolchain has a set of tools, but they are all of known types. It can
have a linker, an assembler, a "clang" (compile, analyze, ...) a non-clang
compiler, etc.

Instead of keeping a map, just have member variable for each type of tool.

llvm-svn: 177479