clang: Fix variable spelling

[urnathan]

Summary

In looking at how TrailingObject worked, I came across this use to crib from. But it spells 'trailing' as 'trailling'. Let's fix that.

Aaron acked this on IRC, so going to commit

[aaron.ballman]

LGTM! Btw, for these sort of "it's a typo" kind of obvious non-functional changes, feel free to commit without posting a phab review if you'd like.

clang/include/clang/AST/DeclCXX.h

                      : ExplicitSpecKind::ResolvedFalse);
   }
 
-  enum TraillingAllocKind {
+  enum TrailingAllocKind {
     TAKInheritsConstructor = 1,
     TAKHasTailExplicit = 1 << 1,
   };
 
-  uint64_t getTraillingAllocKind() const {
+  uint64_t getTrailingAllocKind() const {
     return numTrailingObjects(OverloadToken<InheritedConstructor>()) |
            (numTrailingObjects(OverloadToken<ExplicitSpecifier>()) << 1);
   }

clang/lib/AST/DeclCXX.cpp

 CXXConstructorDecl *CXXConstructorDecl::CreateDeserialized(ASTContext &C,
                                                            unsigned ID,
                                                            uint64_t AllocKind) {
-  bool hasTraillingExplicit = static_cast<bool>(AllocKind & TAKHasTailExplicit);
+  bool hasTrailingExplicit = static_cast<bool>(AllocKind & TAKHasTailExplicit);
   bool isInheritingConstructor =
       static_cast<bool>(AllocKind & TAKInheritsConstructor);
   unsigned Extra =
       additionalSizeToAlloc<InheritedConstructor, ExplicitSpecifier>(
-          isInheritingConstructor, hasTraillingExplicit);
+          isInheritingConstructor, hasTrailingExplicit);
   auto *Result = new (C, ID, Extra) CXXConstructorDecl(
       C, nullptr, SourceLocation(), DeclarationNameInfo(), QualType(), nullptr,
       ExplicitSpecifier(), false, false, ConstexprSpecKind::Unspecified,
       InheritedConstructor(), nullptr);
   Result->setInheritingConstructor(isInheritingConstructor);
   Result->CXXConstructorDeclBits.HasTrailingExplicitSpecifier =
-      hasTraillingExplicit;
+      hasTrailingExplicit;
   Result->setExplicitSpecifier(ExplicitSpecifier());
   return Result;
 }

clang/lib/Serialization/ASTWriterDecl.cpp

 }
 
 void ASTDeclWriter::VisitCXXConstructorDecl(CXXConstructorDecl *D) {
-  Record.push_back(D->getTraillingAllocKind());
+  Record.push_back(D->getTrailingAllocKind());
   addExplicitSpecifier(D->getExplicitSpecifier(), Record);
   if (auto Inherited = D->getInheritedConstructor()) {
     Record.AddDeclRef(Inherited.getShadowDecl());

clang/test/SemaCXX/cxx2a-explicit-bool.cpp

 
 }
 
-namespace trailling_object {
+namespace trailing_object {
 
 template<bool b>
 struct B {