Mirror clang's link stage on Windows.

Fixes problem discussed in rust-lang#811.

[Also deduplicate clang --target argument on Windows, because it's
passed later on in the "// Target flags" section.]

src/lib.rs

@@ -1172,6 +1172,11 @@ impl Build {
                     atlmfc_lib.display()
                 ));
             }
+
+            if compiler.family == ToolFamily::Clang {
+                // Mirror what clang does at link stage
+                self.print(&format_args!("cargo:rustc-link-arg=-defaultlib:oldnames"));
+            }
         }
 
         if self.link_lib_modifiers.is_empty() {
@@ -1758,13 +1763,6 @@ impl Build {
                     cmd.push_opt_unless_duplicate(format!("-O{}", opt_level).into());
                 }
 
-                if cmd.family == ToolFamily::Clang && target.contains("windows") {
-                    // Disambiguate mingw and msvc on Windows. Problem is that
-                    // depending on the origin clang can default to a mismatchig
-                    // run-time.
-                    cmd.push_cc_arg(format!("--target={}", target).into());
-                }
-
                 if cmd.family == ToolFamily::Clang && target.contains("android") {
                     // For compatibility with code that doesn't use pre-defined `__ANDROID__` macro.
                     // If compiler used via ndk-build or cmake (officially supported build methods)