[LLVMgold.so] -plugin-opt=save-temps: save combined module to .lto.o instead of .o

This matches LLD and fixes https://sourceware.org/bugzilla/show_bug.cgi?id=26262#c1

.o is a bad choice for save-temps output because it is easy to override the bitcode file (*.o)

```
 # Use bfd for the example, -fuse-ld=gold is similar.
clang -flto -c a.c  # generate bitcode file a.o
clang -fuse-ld=bfd -flto a.o -o a -Wl,-plugin-opt=save-temps  # override a.o

 # The user repeats the command but get surprised, because a.o is now a combined module.
clang -fuse-ld=bfd -flto a.o -o a -Wl,-plugin-opt=save-temps
```

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D84132

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/tools/gold/gold-plugin.cpp b/llvm/tools/gold/gold-plugin.cpp
index 7654d44..0124e0a 100644
--- a/llvm/tools/gold/gold-plugin.cpp
+++ b/llvm/tools/gold/gold-plugin.cpp
@@ -1050,7 +1050,7 @@ static std::vector<std::pair<SmallString<128>, bool>> runLTO() {
   if (!options::obj_path.empty())
     Filename = options::obj_path;
   else if (options::TheOutputType == options::OT_SAVE_TEMPS)
-    Filename = output_name + ".o";
+    Filename = output_name + ".lto.o";
   else if (options::TheOutputType == options::OT_ASM_ONLY)
     Filename = output_name;
   bool SaveTemps = !Filename.empty();