Rollup merge of rust-lang#68231 - danielframpton:windows-crosscompile, r=alexcrichton

Better support for cross compilation on Windows.

I have been investigating enabling panic=unwind for aarch64-pc-windows-msvc (see rust-lang#65313) and building rustc and cargo hosted on aarch64-pc-windows-msvc.

Without the libpath changes we were trying to link a mix of amd64 and arm64 binaries.

Without the cmake system name change, the llvm build was trying to run an arm64 build tool on the x86_64 build machine.

That said, I haven't tested all different combinations here and am very open to resolving this a different way.

Author: Dylan-DPC

src/bootstrap/native.rs

@@ -230,6 +230,8 @@ impl Step for Llvm {
                 cfg.define("CMAKE_SYSTEM_NAME", "NetBSD");
             } else if target.contains("freebsd") {
                 cfg.define("CMAKE_SYSTEM_NAME", "FreeBSD");
+            } else if target.contains("windows") {
+                cfg.define("CMAKE_SYSTEM_NAME", "Windows");
             }
 
             cfg.define("LLVM_NATIVE_BUILD", builder.llvm_out(builder.config.build).join("build"));

src/librustc_llvm/build.rs

@@ -215,12 +215,14 @@ fn main() {
     let mut cmd = Command::new(&llvm_config);
     cmd.arg(llvm_link_arg).arg("--ldflags");
     for lib in output(&mut cmd).split_whitespace() {
-        if lib.starts_with("-LIBPATH:") {
-            println!("cargo:rustc-link-search=native={}", &lib[9..]);
-        } else if is_crossed {
-            if lib.starts_with("-L") {
+        if is_crossed {
+            if lib.starts_with("-LIBPATH:") {
+                println!("cargo:rustc-link-search=native={}", lib[9..].replace(&host, &target));
+            } else if lib.starts_with("-L") {
                 println!("cargo:rustc-link-search=native={}", lib[2..].replace(&host, &target));
             }
+        } else if lib.starts_with("-LIBPATH:") {
+            println!("cargo:rustc-link-search=native={}", &lib[9..]);
         } else if lib.starts_with("-l") {
             println!("cargo:rustc-link-lib={}", &lib[2..]);
         } else if lib.starts_with("-L") {