[dsymutil] Deduplicate Swift modules by path before copying them (llvm#139342)

(cherry picked from commit 9eeae5a)

Author: adrian-prantl

llvm/test/tools/dsymutil/ARM/swiftmodule.test

@@ -13,6 +13,7 @@
 #
 # CHECK-NOT: Skipping compiled textual Swift interface: {{.*}}/Inputs/Binary.swiftmodule
 # CHECK: Skipping compiled textual Swift interface: {{.*}}/Inputs/FromInterface.swiftmodule
+# CHECK-NOT: Skipping compiled textual Swift interface: {{.*}}/Inputs/FromInterface.swiftmodule
 
 #
 ---
@@ -26,4 +27,8 @@ objects:
     timestamp:       0
     type:            50
     symbols:         []
+  - filename:        '../Inputs/FromInterface.swiftmodule'
+    timestamp:       0
+    type:            50
+    symbols:         []
 ...

llvm/tools/dsymutil/DwarfLinkerForBinary.cpp

@@ -19,6 +19,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/BinaryFormat/MachO.h"
@@ -771,6 +772,7 @@ bool DwarfLinkerForBinary::linkImpl(
         MaxDWARFVersion = std::max(Unit.getVersion(), MaxDWARFVersion);
       };
 
+  llvm::StringSet<> SwiftModules;
   for (const auto &Obj : Map.objects()) {
     // N_AST objects (swiftmodule files) should get dumped directly into the
     // appropriate DWARF section.
@@ -779,6 +781,9 @@ bool DwarfLinkerForBinary::linkImpl(
         outs() << "DEBUG MAP OBJECT: " << Obj->getObjectFilename() << "\n";
 
       StringRef File = Obj->getObjectFilename();
+      if (!SwiftModules.insert(File).second)
+        continue;
+
       auto ErrorOrMem = MemoryBuffer::getFile(File);
       if (!ErrorOrMem) {
         reportWarning("Could not open '" + File + "'");