Sema: have BuildExpressionFromIntegralTemplateArgument produce well-formed IntegerLiterals

BuildExpressionFromIntegralTemplateArgument can produce malformed
IntegerLiterals with an EnumType if the template parameter type
is an EnumType.  This breaks the AST printer which expects all
IntegerLiterals to have a plain integer type.  Instead, give the
IntegerLiteral the enum's promotion type and wrap in an implicit cast
to the EnumType.

llvm-svn: 121862