[lld][Macho] Include dead-stripped symbols in mapfile

ld64 outputs dead stripped symbols when using the -dead-strip flag. This change mimics that behavior for lld.

ld64's -dead_strip flag outputs:
```
$ ld -map map basics.o -o out -dead_strip -L/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib -lSystem
$ cat map
# Path: out
# Arch: x86_64
# Object files:
[  0] linker synthesized
[  1] basics.o
# Sections:
# Address       Size            Segment Section
0x100003F97     0x00000021      __TEXT  __text
0x100003FB8     0x00000048      __TEXT  __unwind_info
0x100004000     0x00000008      __DATA_CONST    __got
0x100008000     0x00000010      __DATA  __ref_section
0x100008010     0x00000001      __DATA  __common
# Symbols:
# Address       Size            File  Name
0x100003F97     0x00000006      [  1] _ref_local
0x100003F9D     0x00000001      [  1] _ref_private_extern
0x100003F9E     0x0000000C      [  1] _main
0x100003FAA     0x00000006      [  1] _no_dead_strip_globl
0x100003FB0     0x00000001      [  1] _ref_from_no_dead_strip_globl
0x100003FB1     0x00000006      [  1] _no_dead_strip_local
0x100003FB7     0x00000001      [  1] _ref_from_no_dead_strip_local
0x100003FB8     0x00000048      [  0] compact unwind info
0x100004000     0x00000008      [  0] non-lazy-pointer-to-local: _ref_com
0x100008000     0x00000008      [  1] _ref_data
0x100008008     0x00000008      [  1] l_ref_data
0x100008010     0x00000001      [  1] _ref_com

# Dead Stripped Symbols:
#               Size            File  Name
<<dead>>        0x00000006      [  1] _unref_extern
<<dead>>        0x00000001      [  1] _unref_local
<<dead>>        0x00000007      [  1] _unref_private_extern
<<dead>>        0x00000001      [  1] _ref_private_extern_u
<<dead>>        0x00000008      [  1] _unref_data
<<dead>>        0x00000008      [  1] l_unref_data
<<dead>>        0x00000001      [  1] _unref_com
```

Reviewed By: int3, #lld-macho, thevinster

Differential Revision: https://reviews.llvm.org/D114737

0 files changed, 0 insertions, 0 deletions