[ORC] De-duplicate some logic for handling MachO::dylib-based load commands.

All such commands share a common struct layout, and we'll be introducing
another soon (LC_LOAD_WEAK_DYLIB). To avoid redundant specializations this
commit moves the logic for these commands into a common base class.

Author: lhames

llvm/include/llvm/ExecutionEngine/Orc/MachOBuilder.h

@@ -81,22 +81,22 @@ struct MachOBuilderLoadCommand
       : MachOBuilderLoadCommandImplBase<LCType>(std::forward<ArgTs>(Args)...) {}
 };
 
-template <>
-struct MachOBuilderLoadCommand<MachO::LC_ID_DYLIB>
-    : public MachOBuilderLoadCommandImplBase<MachO::LC_ID_DYLIB> {
+template <MachO::LoadCommandType LCType>
+struct MachOBuilderDylibLoadCommand
+    : public MachOBuilderLoadCommandImplBase<LCType> {
 
-  MachOBuilderLoadCommand(std::string Name, uint32_t Timestamp,
-                          uint32_t CurrentVersion,
-                          uint32_t CompatibilityVersion)
-      : MachOBuilderLoadCommandImplBase(
+  MachOBuilderDylibLoadCommand(std::string Name, uint32_t Timestamp,
+                               uint32_t CurrentVersion,
+                               uint32_t CompatibilityVersion)
+      : MachOBuilderLoadCommandImplBase<LCType>(
             MachO::dylib{24, Timestamp, CurrentVersion, CompatibilityVersion}),
         Name(std::move(Name)) {
-    cmdsize += (this->Name.size() + 1 + 3) & ~0x3;
+    this->cmdsize += (this->Name.size() + 1 + 3) & ~0x3;
   }
 
   size_t write(MutableArrayRef<char> Buf, size_t Offset,
                bool SwapStruct) override {
-    Offset = writeMachOStruct(Buf, Offset, rawStruct(), SwapStruct);
+    Offset = writeMachOStruct(Buf, Offset, this->rawStruct(), SwapStruct);
     strcpy(Buf.data() + Offset, Name.data());
     return Offset + ((Name.size() + 1 + 3) & ~0x3);
   }
@@ -105,26 +105,15 @@ struct MachOBuilderLoadCommand<MachO::LC_ID_DYLIB>
 };
 
 template <>
-struct MachOBuilderLoadCommand<MachO::LC_LOAD_DYLIB>
-    : public MachOBuilderLoadCommandImplBase<MachO::LC_LOAD_DYLIB> {
-
-  MachOBuilderLoadCommand(std::string Name, uint32_t Timestamp,
-                          uint32_t CurrentVersion,
-                          uint32_t CompatibilityVersion)
-      : MachOBuilderLoadCommandImplBase(
-            MachO::dylib{24, Timestamp, CurrentVersion, CompatibilityVersion}),
-        Name(std::move(Name)) {
-    cmdsize += (this->Name.size() + 1 + 3) & ~0x3;
-  }
-
-  size_t write(MutableArrayRef<char> Buf, size_t Offset,
-               bool SwapStruct) override {
-    Offset = writeMachOStruct(Buf, Offset, rawStruct(), SwapStruct);
-    strcpy(Buf.data() + Offset, Name.data());
-    return Offset + ((Name.size() + 1 + 3) & ~0x3);
-  }
+struct MachOBuilderLoadCommand<MachO::LC_ID_DYLIB>
+    : public MachOBuilderDylibLoadCommand<MachO::LC_ID_DYLIB> {
+  using MachOBuilderDylibLoadCommand::MachOBuilderDylibLoadCommand;
+};
 
-  std::string Name;
+template <>
+struct MachOBuilderLoadCommand<MachO::LC_LOAD_DYLIB>
+    : public MachOBuilderDylibLoadCommand<MachO::LC_LOAD_DYLIB> {
+  using MachOBuilderDylibLoadCommand::MachOBuilderDylibLoadCommand;
 };
 
 template <>