Introduce an ArchiveBuilderBuilder

This avoids monomorphizing all linker code for each codegen backend and
will allow passing in extra information to the archive builder from the
codegen backend.

compiler/rustc_codegen_llvm/src/back/archive.rs

@@ -10,7 +10,7 @@ use std::str;
 
 use crate::llvm::archive_ro::{ArchiveRO, Child};
 use crate::llvm::{self, ArchiveKind, LLVMMachineType, LLVMRustCOFFShortExport};
-use rustc_codegen_ssa::back::archive::ArchiveBuilder;
+use rustc_codegen_ssa::back::archive::{ArchiveBuilder, ArchiveBuilderBuilder};
 use rustc_session::cstore::{DllCallingConvention, DllImport};
 use rustc_session::Session;
 
@@ -53,16 +53,11 @@ fn llvm_machine_type(cpu: &str) -> LLVMMachineType {
 }
 
 impl<'a> ArchiveBuilder<'a> for LlvmArchiveBuilder<'a> {
-    /// Creates a new static archive, ready for modifying the archive specified
-    /// by `config`.
-    fn new(sess: &'a Session) -> LlvmArchiveBuilder<'a> {
-        LlvmArchiveBuilder { sess, additions: Vec::new() }
-    }
-
-    fn add_archive<F>(&mut self, archive: &Path, skip: F) -> io::Result<()>
-    where
-        F: FnMut(&str) -> bool + 'static,
-    {
+    fn add_archive(
+        &mut self,
+        archive: &Path,
+        skip: Box<dyn FnMut(&str) -> bool + 'static>,
+    ) -> io::Result<()> {
         let archive_ro = match ArchiveRO::open(archive) {
             Ok(ar) => ar,
             Err(e) => return Err(io::Error::new(io::ErrorKind::Other, e)),
@@ -87,14 +82,23 @@ impl<'a> ArchiveBuilder<'a> for LlvmArchiveBuilder<'a> {
 
     /// Combine the provided files, rlibs, and native libraries into a single
     /// `Archive`.
-    fn build(mut self, output: &Path) -> bool {
+    fn build(mut self: Box<Self>, output: &Path) -> bool {
         match self.build_with_llvm(output) {
             Ok(any_members) => any_members,
             Err(e) => self.sess.fatal(&format!("failed to build archive: {}", e)),
         }
     }
+}
+
+pub struct LlvmArchiveBuilderBuilder;
+
+impl ArchiveBuilderBuilder for LlvmArchiveBuilderBuilder {
+    fn new_archive_builder<'a>(&self, sess: &'a Session) -> Box<dyn ArchiveBuilder<'a> + 'a> {
+        Box::new(LlvmArchiveBuilder { sess, additions: Vec::new() })
+    }
 
     fn create_dll_import_lib(
+        &self,
         sess: &Session,
         lib_name: &str,
         dll_imports: &[DllImport],