[llvm-dwarfdump] Display DW_AT_high_pc as absolute value

DWARF4 relative DW_AT_high_pc values are now displayed as absolute
addresses. The relative value is only shown when explicitly dumping the
forms, i.e. in show-form or verbose mode.

```
DW_AT_low_pc	(0x0000000000000049)
DW_AT_high_pc	(0x00000019)
```

becomes

```
DW_AT_low_pc	(0x0000000000000049)
DW_AT_high_pc	(0x0000000000000062)
```

Differential revision: https://reviews.llvm.org/D40317

rdar://35416943

llvm-svn: 319044