`GlobalValue::get_section` can segfault if there is no section on the global

Describe the Bug LLVMGetSection returns a null pointer if the global does not have a section set on it. This means that GlobalValue::get_section should return Option<&CStr> rather than &CStr, and check whether null was returned and return None in that case. Similarly, GlobalValue::set_section should take Option<&CStr> to allow you to remove the section by passing None.

To Reproduce Get a handle to a GlobalValue with no section set. Call get_section() on it. Segfault.

Expected Behavior Function should check whether LLVMGetSection returns null.

LLVM Version (please complete the following information):

• LLVM Version: 10
• Inkwell Branch Used: master

Desktop (please complete the following information): Windows 10

Additional Context N/A