Filter out -nolibc warning with MingW Clang

Author: jyn514

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -692,6 +692,15 @@ fn is_windows_gnu_ld(sess: &Session) -> bool {
     sess.target.is_like_windows
         && !sess.target.is_like_msvc
         && matches!(flavor, LinkerFlavor::Gnu(_, Lld::No))
+        && sess.target.abi != Abi::Llvm
+}
+
+fn is_windows_gnu_clang(sess: &Session) -> bool {
+    let (_, flavor) = linker_and_flavor(sess);
+    sess.target.is_like_windows
+        && !sess.target.is_like_msvc
+        && matches!(flavor, LinkerFlavor::Gnu(Cc::Yes, Lld::No))
+        && sess.target.abi == Abi::Llvm
 }
 
 fn report_linker_output(sess: &Session, levels: CodegenLintLevels, stdout: &[u8], stderr: &[u8]) {
@@ -781,7 +790,18 @@ fn report_linker_output(sess: &Session, levels: CodegenLintLevels, stdout: &[u8]
                 *output += "\n"
             }
         });
-    }
+    } else if is_windows_gnu_clang(sess) {
+        info!("inferred Windows Clang (GNU ABI)");
+        escaped_stderr = for_each(&stderr, |line, output| {
+            if line.contains("argument unused during compilation: '-nolibc'") {
+                linker_info += line;
+                linker_info += "\n";
+            } else {
+                *output += line;
+                *output += "\n"
+            }
+        });
+    };
 
     let lint_msg = |msg| {
         emit_lint_base(

src/tools/compiletest/src/directives/directive_names.rs

@@ -142,6 +142,7 @@ pub(crate) const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "ignore-x86_64",
     "ignore-x86_64-apple-darwin",
     "ignore-x86_64-pc-windows-gnu",
+    "ignore-x86_64-pc-windows-gnullvm",
     "ignore-x86_64-unknown-linux-gnu",
     "incremental",
     "known-bug",
@@ -263,6 +264,7 @@ pub(crate) const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "only-x86_64-apple-darwin",
     "only-x86_64-fortanix-unknown-sgx",
     "only-x86_64-pc-windows-gnu",
+    "only-x86_64-pc-windows-gnullvm",
     "only-x86_64-pc-windows-msvc",
     "only-x86_64-unknown-linux-gnu",
     "pp-exact",

tests/ui/linking/no-libc-mingw-llvm.rs

@@ -0,0 +1,8 @@
+//@ build-pass
+//@ only-x86_64-pc-windows-gnullvm
+#![allow(linker_messages)]
+#![warn(linker_info)]
+
+//~? WARN argument unused
+
+fn main() {}

tests/ui/linking/no-libc-mingw-llvm.stderr

@@ -0,0 +1,11 @@
+warning: clang: warning: argument unused during compilation: '-nolibc' [-Wunused-command-line-argument]
+         
+   |
+note: the lint level is defined here
+  --> $DIR/no-libc-mingw-llvm.rs:7:9
+   |
+LL | #![warn(linker_info)]
+   |         ^^^^^^^^^^^
+
+warning: 1 warning emitted
+