Let clang-format break after a function's return type.

Before:
TypeSpecDecl *TypeSpecDecl::Create(ASTContext &C, DeclContext *DC,
                                   SourceLocation L, IdentifierInfo *II,
                                   Type *T) {}

After:
TypeSpecDecl *
TypeSpecDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation L,
                     IdentifierInfo *II, Type *T) {}

This fixes llvm.org/PR14717.