Link with libc++ instead of libstdc++. This avoids undefined reference to std::__1 errors.

diff --git a/rustc-1.29.0-src/compiler/rustc_llvm/build.rs b/rustc-1.29.0-src/compiler/rustc_llvm/build.rs
index 1619637..6ec0f83 100644
--- a/rustc-1.29.0-src/compiler/rustc_llvm/build.rs
+++ b/rustc-1.29.0-src/compiler/rustc_llvm/build.rs
@@ -248,7 +248,7 @@ fn main() {
         // NetBSD uses a separate library when relocation is required
         "stdc++_pic"
     } else {
-        "stdc++"
+        "c++"
     };
 
     // C++ runtime library