[lld-macho] Fix warning

```
/Users/ksmiley/dev/llvm-project/lld/MachO/Symbols.cpp:43:27: warning: field 'external' will be initialized after field 'weakDefCanBeHidden' [-Wreorder-ctor]
      weakDef(isWeakDef), external(isExternal),
                          ^
1 warning generated.
```

Differential Revision: https://reviews.llvm.org/D113823

GitOrigin-RevId: 51715fbd96c100e08ad5e0afe78eff474e4caa3f
diff --git a/MachO/Symbols.cpp b/MachO/Symbols.cpp
index 7b04d25..ed9b4d6 100644
--- a/MachO/Symbols.cpp
+++ b/MachO/Symbols.cpp
@@ -40,8 +40,8 @@
       overridesWeakDef(canOverrideWeakDef), privateExtern(isPrivateExtern),
       includeInSymtab(true), thumb(isThumb),
       referencedDynamically(isReferencedDynamically), noDeadStrip(noDeadStrip),
-      weakDef(isWeakDef), external(isExternal),
-      weakDefCanBeHidden(isWeakDefCanBeHidden) {
+      weakDefCanBeHidden(isWeakDefCanBeHidden), weakDef(isWeakDef),
+      external(isExternal) {
   if (isec) {
     isec->symbols.push_back(this);
     // Maintain sorted order.