gn build: (manually) Port ae032e27 and 21f83113.

__register_frame and __deregister_frame are associated with the
.eh_frame section, which I think is used on all of our platforms
except Windows and 32-bit ARM (which uses the ARM EHABI).

Also add a file that was added to lld/MachO.

llvm/utils/gn/secondary/lld/MachO/BUILD.gn

@@ -28,6 +28,7 @@ static_library("MachO2") {
     "ExportTrie.cpp",
     "InputFiles.cpp",
     "InputSection.cpp",
+    "LTO.cpp",
     "MergedOutputSection.cpp",
     "ObjC.cpp",
     "OutputSection.cpp",

llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn

@@ -190,6 +190,18 @@ write_cmake_config("config") {
     ]
   }
 
+  if (current_os == "win" || current_cpu == "arm") {
+    values += [
+      "HAVE_DEREGISTER_FRAME=",
+      "HAVE_REGISTER_FRAME=",
+    ]
+  } else {
+    values += [
+      "HAVE_DEREGISTER_FRAME=1",
+      "HAVE_REGISTER_FRAME=1",
+    ]
+  }
+
   if (current_os == "win") {
     values += [
       "HAVE_DECL_STRERROR_S=1",