[AArch64] Add some CPU targets for "generic", A-53 and A-57.

Enables the clang driver to begin targeting specific CPUs. Introduced a
"generic" CPU which will ensure that the optional FP feature is enabled
by default when it gets to LLVM, without needing any extra arguments.
Cortex-A53 and A-57 are also introduced with tests, although backend
handling of them does not yet exist.

llvm-svn: 193740
diff --git a/clang/lib/Driver/Tools.h b/clang/lib/Driver/Tools.h
index 4a0626d..d5b2848 100644
--- a/clang/lib/Driver/Tools.h
+++ b/clang/lib/Driver/Tools.h
@@ -49,6 +49,8 @@
                                  const InputInfo &Output,
                                  const InputInfoList &Inputs) const;
 
+    void AddAArch64TargetArgs(const llvm::opt::ArgList &Args,
+                              llvm::opt::ArgStringList &CmdArgs) const;
     void AddARMTargetArgs(const llvm::opt::ArgList &Args,
                           llvm::opt::ArgStringList &CmdArgs,
                           bool KernelOrKext) const;