Sema: remove unnecessary parameter for SwiftName handling (NFCI)

This code never actually did anything in the implementation.

`mergeDeclAttribute` is declared as `static`, and referenced exactly
once in the file: from `Sema::mergeDeclAttributes`.

`Sema::mergeDeclAttributes` sets `LocalAMK` to `AMK_None`.  If the
attribute is `DeprecatedAttr`, `UnavailableAttr`, or `AvailabilityAttr`
then the `LocalAMK` is updated.  However, because we are dealing with a
`SwiftNameDeclAttr` here, `LocalAMK` remains `AMK_None`.  This is then
passed to the function which will as a result pass the value of
`AMK_None == AMK_Override` aka `false`.  Simply propagate the value
through and erase the dead codepath.

Thanks to Aaron Ballman for flagging the use of the availability merge
kind here leading to this simplification!

Differential Revision: https://reviews.llvm.org/D88263
Reviewed By: Aaron Ballman

Author: compnerd

clang/include/clang/Sema/Sema.h

@@ -3070,7 +3070,7 @@ class Sema final {
   mergeSpeculativeLoadHardeningAttr(Decl *D,
                                     const SpeculativeLoadHardeningAttr &AL);
   SwiftNameAttr *mergeSwiftNameAttr(Decl *D, const SwiftNameAttr &SNA,
-                                    StringRef Name, bool Override);
+                                    StringRef Name);
   OptimizeNoneAttr *mergeOptimizeNoneAttr(Decl *D,
                                           const AttributeCommonInfo &CI);
   InternalLinkageAttr *mergeInternalLinkageAttr(Decl *D, const ParsedAttr &AL);

clang/lib/Sema/SemaDecl.cpp

@@ -2593,8 +2593,7 @@ static bool mergeDeclAttribute(Sema &S, NamedDecl *D,
   } else if (const auto *MA = dyn_cast<MinSizeAttr>(Attr))
     NewAttr = S.mergeMinSizeAttr(D, *MA);
   else if (const auto *SNA = dyn_cast<SwiftNameAttr>(Attr))
-    NewAttr = S.mergeSwiftNameAttr(D, *SNA, SNA->getName(),
-                                   AMK == Sema::AMK_Override);
+    NewAttr = S.mergeSwiftNameAttr(D, *SNA, SNA->getName());
   else if (const auto *OA = dyn_cast<OptimizeNoneAttr>(Attr))
     NewAttr = S.mergeOptimizeNoneAttr(D, *OA);
   else if (const auto *InternalLinkageA = dyn_cast<InternalLinkageAttr>(Attr))

clang/lib/Sema/SemaDeclAttr.cpp

@@ -4282,13 +4282,8 @@ NoSpeculativeLoadHardeningAttr *Sema::mergeNoSpeculativeLoadHardeningAttr(
 }
 
 SwiftNameAttr *Sema::mergeSwiftNameAttr(Decl *D, const SwiftNameAttr &SNA,
-                                        StringRef Name, bool Override) {
+                                        StringRef Name) {
   if (const auto *PrevSNA = D->getAttr<SwiftNameAttr>()) {
-    if (Override) {
-      // FIXME: warn about incompatible override
-      return nullptr;
-    }
-
     if (PrevSNA->getName() != Name && !PrevSNA->isImplicit()) {
       Diag(PrevSNA->getLocation(), diag::err_attributes_are_not_compatible)
           << PrevSNA << &SNA;