Change LLVM bitcode linking to use tree reduction to scale better

llvm/tools/lto/lto.cpp

Index: llvm/tools/lto/lto.cpp
===================================================================
--- a/llvm/tools/lto/lto.cpp
+++ b/llvm/tools/lto/lto.cpp
@@ -205,6 +205,16 @@
   return cg->addModule(mod, sLastErrorString);
 }
 
+// @LOCALMOD-BEGIN
+bool lto_codegen_gather_module(lto_code_gen_t cg, lto_module_t mod) {
+  return cg->gatherModule(mod);
+}
+
+bool lto_codegen_link_gathered_modules_and_dispose(lto_code_gen_t cg) {
+  return cg->linkGatheredModulesAndDispose(sLastErrorString);
+}
+// @LOCALMOD-END
+
 /// lto_codegen_set_debug_model - Sets what if any format of debug info should
 /// be generated. Returns true on error (check lto_get_error_message() for
 /// details).
@@ -343,4 +353,3 @@
 void lto_codegen_debug_options(lto_code_gen_t cg, const char *opt) {
   cg->setCodeGenDebugOptions(opt);
 }
-