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.

src/rustllvm/RustWrapper.cpp

@@ -803,3 +803,10 @@ extern "C" void LLVMDICompositeTypeSetTypeArray(
 {
     unwrapDI<DICompositeType>(CompositeType).setTypeArray(unwrapDI<DIArray>(TypeArray));
 }
+
+extern "C" char *LLVMTypeToString(LLVMTypeRef Type) {
+    std::string s;
+    llvm::raw_string_ostream os(s);
+    unwrap<llvm::Type>(Type)->print(os);
+    return strdup(os.str().data());
+}