Mirror clang's link stage on Windows.

cc-test/build.rs

@@ -7,6 +7,12 @@ fn main() {
     fs::remove_dir_all(&out).unwrap();
     fs::create_dir(&out).unwrap();
 
+    let target = std::env::var("TARGET").unwrap();
+
+    if target.ends_with("msvc") {
+        env::set_var("CL", "-Zl"); // drop linker directives
+    }
+
     cc::Build::new()
         .file("src/foo.c")
         .flag_if_supported("-Wall")
@@ -21,7 +27,6 @@ fn main() {
         .include("src/include")
         .compile("bar");
 
-    let target = std::env::var("TARGET").unwrap();
     let file = target.split("-").next().unwrap();
     let file = format!(
         "src/{}.{}",
@@ -55,6 +60,14 @@ fn main() {
 
     if target.contains("windows") {
         cc::Build::new().file("src/windows.c").compile("windows");
+        if target.ends_with("msvc") && which::which("clang").is_ok() {
+            cc::Build::new()
+                .compiler("clang")
+                .define("_CRT_NONSTDC_NO_WARNINGS", None)
+                .file("src/msvcrt.c")
+                .compile("nonstdcrt");
+            println!("cargo:rustc-cfg=feature=\"msvcrt\"");
+        }
     }
 
     // Test that the `windows_registry` module will set PATH by looking for

cc-test/src/NMakefile

@@ -2,13 +2,12 @@ all: $(OUT_DIR)/msvc.lib $(OUT_DIR)/msvc.exe
 
 $(OUT_DIR)/msvc.lib: $(OUT_DIR)/msvc.o
 	lib -nologo -out:$(OUT_DIR)/msvc.lib $(OUT_DIR)/msvc.o
-	rc -h
 
 $(OUT_DIR)/msvc.o: src/msvc.c
 	$(CC) -nologo -c -Fo:$@ src/msvc.c -MD
 
 $(OUT_DIR)/msvc.exe: $(OUT_DIR)/msvc2.o
-	$(CC) -nologo -Fo:$@ $(OUT_DIR)/msvc2.o
+	$(CC) -nologo -Fo:$@ $(OUT_DIR)/msvc2.o /link msvcrt.lib
 
 $(OUT_DIR)/msvc2.o: src/msvc.c
 	$(CC) -nologo -c -Fo:$@ src/msvc.c -DMAIN -MD

cc-test/src/msvcrt.c

@@ -0,0 +1,3 @@
+#include <stdlib.h>
+#include <string.h>
+void msvcrt() { free(strdup("")); }

cc-test/tests/all.rs

@@ -50,6 +50,17 @@ fn msvc_here() {
     }
 }
 
+#[test]
+#[cfg(feature = "msvcrt")]
+fn msvcrt_here() {
+    extern "C" {
+        fn msvcrt();
+    }
+    unsafe {
+        msvcrt();
+    }
+}
+
 #[test]
 fn opt_linkage() {
     unsafe {

src/lib.rs

@@ -1171,6 +1171,11 @@ 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() {
@@ -1712,13 +1717,6 @@ 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)