[clang] [MinGW] Pass LTO options to the linker

This matches what is done on other platforms too.

This fixes one part of
mstorsjo/llvm-mingw#349.

Differential Revision: https://reviews.llvm.org/D158411

Author: mstorsjo

clang/lib/Driver/ToolChains/MinGW.cpp

@@ -238,6 +238,12 @@ void tools::MinGW::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   AddLinkerInputs(TC, Inputs, Args, CmdArgs, JA);
 
+  if (D.isUsingLTO()) {
+    assert(!Inputs.empty() && "Must have at least one input.");
+    addLTOOptions(TC, Args, CmdArgs, Output, Inputs[0],
+                  D.getLTOMode() == LTOK_Thin);
+  }
+
   if (C.getDriver().IsFlangMode()) {
     addFortranRuntimeLibraryPath(TC, Args, CmdArgs);
     addFortranRuntimeLibs(TC, CmdArgs);

clang/test/Driver/mingw-lto.c

@@ -1,4 +1,6 @@
 // The default linker doesn't support LLVM bitcode
 // RUN: not %clang --target=i686-pc-windows-gnu %s -flto -fuse-ld=bfd
 // When using lld, this is allowed though.
-// RUN: %clang --target=i686-pc-windows-gnu -### %s -flto -fuse-ld=lld -B%S/Inputs/lld
+// RUN: %clang --target=i686-pc-windows-gnu -### %s -flto -fuse-ld=lld -B%S/Inputs/lld -femulated-tls 2>&1 | FileCheck %s
+
+// CHECK: "-plugin-opt=-emulated-tls"