[Driver] Reland again again: Default Android toolchains to libc++.

Landed more fixes to the compiler-rt Android tests.

Original review was https://reviews.llvm.org/D53109.

llvm-svn: 346167
diff --git a/clang/lib/Driver/ToolChains/Linux.h b/clang/lib/Driver/ToolChains/Linux.h
index 2f0c361..4a662cb 100644
--- a/clang/lib/Driver/ToolChains/Linux.h
+++ b/clang/lib/Driver/ToolChains/Linux.h
@@ -37,6 +37,7 @@
                           llvm::opt::ArgStringList &CC1Args) const override;
   void AddIAMCUIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                            llvm::opt::ArgStringList &CC1Args) const override;
+  CXXStdlibType GetDefaultCXXStdlibType() const override;
   bool isPIEDefault() const override;
   bool IsMathErrnoDefault() const override;
   SanitizerMask getSupportedSanitizers() const override;