Enable unwind support for all non-official builds

This makes unwind support consistent on Linux (used by
base::debug::StackTrace). A combination of arch-specific toolchain defaults
and arch-specific cflags made the previous behavior inconsistent.

Unwind tables are useful for development and much cheaper than
debuginfo, so enable them for all non-official builds.

TEST=build for ia32, x64, arm (compared defaults & official)
BUG=180975

Review URL: https://codereview.chromium.org/129283003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243919 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243919