have LLVM print type strings for us

Example:

    void ({ i64, %tydesc*, i8*, i8*, i8 }*, i64*, %"struct.std::fmt::Formatter[#1]"*)*

Before, we would print 20 levels deep due to recursion in the type
definition.
auto merge of #9815 : thestinger/rust/type, r=huonw

Example:

    void ({ i64, %tydesc*, i8*, i8*, i8 }*, i64*, %"struct.std::fmt::Formatter[#1]"*)*

Before, we would print 20 levels deep due to recursion in the type
definition.