Improve debug support

[dz333]

From @gharrma on February 11, 2018 16:19

Improve debug support by

• Providing debug type information for class fields
• Limiting variable information to their lexical scope

Copied from original issue: gharrma/polyllvm#35

[dz333]

From @gharrma on May 24, 2018 17:23

Note: with gdb we were able to print the values of local variables. Recently I switched to using lldb (since gdb seems to have decreasing support on Mac), and it appears that lldb is not able to print variable values. This likely indicates that something is off in the debug information emitted for local variables.