rustc: Add suffix ".rc" to LLVM module identifier

LLVM code generator emits the ".file filename" directive for ELF
backends. Value of the "filename" is set as the LLVM module identifier.
Due to a LLVM MC bug[1], LLVM crashes if the module identifer is same as
other symbols such as a function name in the module.

This patch adds a ".rc" suffix (means crates) to LLVM module identifier
to workaround the bug.

Fixes issue #1251.

1. http://llvm.org/bugs/show_bug.cgi?id=11479

src/comp/middle/trans.rs

@@ -6059,7 +6059,18 @@ fn trans_crate(sess: session::session, crate: @ast::crate, tcx: ty::ctxt,
     -> ModuleRef {
     let sha = std::sha1::mk_sha1();
     let link_meta = link::build_link_meta(sess, *crate, output, sha);
-    let llmod = str::as_buf(link_meta.name, {|buf|
+
+    // Append ".rc" to crate name as LLVM module identifier.
+    //
+    // LLVM code generator emits a ".file filename" directive
+    // for ELF backends. Value of the "filename" is set as the
+    // LLVM module identifier.  Due to a LLVM MC bug[1], LLVM
+    // crashes if the module identifer is same as other symbols
+    // such as a function name in the module. 
+    // 1. http://llvm.org/bugs/show_bug.cgi?id=11479
+    let llmod_id = link_meta.name + ".rc";
+
+    let llmod = str::as_buf(llmod_id, {|buf|
         llvm::LLVMModuleCreateWithNameInContext
             (buf, llvm::LLVMGetGlobalContext())
     });

src/test/run-pass/issue-1251.rs

@@ -0,0 +1,7 @@
+#[link(name = "unsupervise")];
+
+native mod rustrt {
+      fn unsupervise();
+}
+
+fn main() { }