MachOImageSymbolTableReader: permit indirect symbols to exist among external defined symbols

MachOImageSymbolTableReader: permit indirect symbols to exist among
external defined symbols.

Indirect symbols remain unsupported.

Xcode 5.1 ld64-236.3/src/ld/LinkEditClassic.hpp
ld::tool::SymbolTableAtom<>::addGlobal() is responsible for producing
symbols found in the extdef portion of the symbol table. It always sets
the type to N_ABS, N_SECT, or N_INDR, each with the N_EXT bit set. The
N_PEXT bit is never set for non-object files, and we’re not concerned
with reading object files. With this change to tolerate N_INDR, I think
we’re covering all of the symbol types that we might find ld writing to
the extdef portion of the symbol table.

https://groups.google.com/a/chromium.org/forum/#!topic/crashpad-dev/k7QkLwO71Zo

R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/878400947fee0b0f5398ea38e7f5e7dfd330b109

[Mark Mentovai, 2015-02-04 23:37:23]

mark@chromium.org changed reviewers:
+ rsesek@chromium.org

[Robert Sesek, 2015-02-05 17:37:43]

LGTM

[Mark Mentovai, 2015-02-05 18:39:25]

Committed patchset #2 (id:20001) manually as
878400947fee0b0f5398ea38e7f5e7dfd330b109 (presubmit successful).