Fix that AlignedAllocation.h doesn't compile because of VersionTuple

[teemperor]

Summary

rL334399 put VersionTuple in the llvm namespace, but this header still assumes it's in the clang namespace.
This leads to compilation failures with enabled modules when building Clang.

include/clang/Basic/AlignedAllocation.h

 #define LLVM_CLANG_BASIC_ALIGNED_ALLOCATION_H
 
 #include "llvm/ADT/Triple.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/VersionTuple.h"
 
 namespace clang {
 
-inline VersionTuple alignedAllocMinVersion(llvm::Triple::OSType OS) {
+inline llvm::VersionTuple alignedAllocMinVersion(llvm::Triple::OSType OS) {
   switch (OS) {
   default:
     break;
   case llvm::Triple::Darwin:
   case llvm::Triple::MacOSX: // Earliest supporting version is 10.13.
-    return VersionTuple(10U, 13U);
+    return llvm::VersionTuple(10U, 13U);
   case llvm::Triple::IOS:
   case llvm::Triple::TvOS: // Earliest supporting version is 11.0.0.
-    return VersionTuple(11U);
+    return llvm::VersionTuple(11U);
   case llvm::Triple::WatchOS: // Earliest supporting version is 4.0.0.
-    return VersionTuple(4U);
+    return llvm::VersionTuple(4U);
   }
 
   llvm_unreachable("Unexpected OS");
 }
 
 } // end namespace clang
 
 #endif // LLVM_CLANG_BASIC_ALIGNED_ALLOCATION_H