[lldb] Encode bool as unsigned int
bool is considered to be unsigned according to std::is_unsigned<bool>::value (and Type::GetTypeInfo). Encoding it as signed int works fine for normal variables and fields, but breaks when reading the values of boolean bitfields. If the field is declared as bool b : 1 and has a value of 0b1, the call to SBValue::GetValueAsSigned() will return -1.
Reviewed By: teemperor
Differential Revision: https://reviews.llvm.org/D102685