[LTO API] add lto_codegen_set_should_internalize.

When debugging LTO issues with ld64, we use -save-temps to save the merged
optimized bitcode file, then invoke ld64 again on the single bitcode file.
The saved bitcode file is already internalized, so we can call
lto_codegen_set_should_internalize and skip running internalization again.

rdar://20227235


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235211 91177308-0d34-0410-b5e6-96231b3b80d8

tools/lto/lto.cpp

@@ -333,3 +333,8 @@ void lto_codegen_debug_options(lto_code_gen_t cg, const char *opt) {
 }
 
 unsigned int lto_api_version() { return LTO_API_VERSION; }
+
+void lto_codegen_set_should_internalize(lto_code_gen_t cg,
+                                        bool ShouldInternalize) {
+  unwrap(cg)->setShouldInternalize(ShouldInternalize);
+}