[Driver] Add driver support for Fuchsia

Provide toolchain and tool support for Fuchsia operating system.
Fuchsia uses compiler-rt as the runtime library and libc++, libc++abi
and libunwind as the C++ standard library. lld is used as a default
linker.

Differential Revision: https://reviews.llvm.org/D25117

llvm-svn: 283420
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 1a6f27d..f26d61f 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -3075,6 +3075,9 @@
     case llvm::Triple::NaCl:
       TC = new toolchains::NaClToolChain(*this, Target, Args);
       break;
+    case llvm::Triple::Fuchsia:
+      TC = new toolchains::Fuchsia(*this, Target, Args);
+      break;
     case llvm::Triple::Solaris:
       TC = new toolchains::Solaris(*this, Target, Args);
       break;