[DebugInfo][Clang] record the access flag for class/struct/union types.

Summary: This patch records the access flag for
class/struct/union types in the clang part.

The summary of binary size change and debug info size change due to the DW_AT_accessibility attribute are as the following table. They are built with flags of `clang -O0 -g` (no -gz).

| section | before | after | change | % |
| .debug_loc | 929821 | 929821 |0|0|
|.debug_abbrev | 5885289 | 5971547 |+86258|+1.466%|
|.debug_info | 497613455 | 498122074 |+508619|+0.102%|
|.debug_ranges | 45731664 | 45731664 |0|0|
|.debug_str | 233842595 | 233839388 |-3207| -0.001%|
|.debug_line | 149773166 | 149764583 |-8583|-0.006%|
|total (debug) |933775990 |934359077|+583087 |+0.062%|

|total (binary) |1394617288 | 1395200024| +582736|+0.042%|

Reviewed By: dblaikie, shchenz

Differential Revision: https://reviews.llvm.org/D115503