Port Instrument coverage requires llvm 12 to the new struct

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -1,5 +1,6 @@
 use crate::common::CodegenCx;
 use crate::coverageinfo;
+use crate::errors::InstrumentCoverageRequiresLLVM12;
 use crate::llvm;
 
 use llvm::coverageinfo::CounterMappingRegion;
@@ -37,7 +38,7 @@ pub fn finalize<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) {
     // LLVM 12.
     let version = coverageinfo::mapping_version();
     if version < 4 {
-        tcx.sess.fatal("rustc option `-C instrument-coverage` requires LLVM 12 or higher.");
+        tcx.sess.emit_fatal(InstrumentCoverageRequiresLLVM12);
     }
 
     debug!("Generating coverage map for CodegenUnit: `{}`", cx.codegen_unit.name());

compiler/rustc_codegen_llvm/src/errors.rs

@@ -42,3 +42,7 @@ pub(crate) struct ErrorCreatingImportLibrary<'a> {
     pub lib_name: &'a str,
     pub error: String,
 }
+
+#[derive(SessionDiagnostic)]
+#[diag(codegen_llvm::instrument_coverage_requires_llvm_12)]
+pub(crate) struct InstrumentCoverageRequiresLLVM12;

compiler/rustc_error_messages/locales/en-US/codegen_llvm.ftl

@@ -15,3 +15,6 @@ codegen_llvm_unknown_feature_fill_request =
 
 codegen_llvm_error_creating_import_library =
     Error creating import library for {$lib_name}: {$error}
+
+codegen_llvm_instrument_coverage_requires_llvm_12 =
+    rustc option `-C instrument-coverage` requires LLVM 12 or higher.