crash_dump: Fix addr2line output parsing wrt ':'
crash_dump: Fix addr2line output parsing wrt ':'

On Windows, the old x86 toolchain's binutils is built with Cygwin, while
the PNaCl/nacl-clang toolchain's binutils is built with MinGW.  This
means that tools like addr2line differ between toolchains in how they
print file names: Cygwin pseudo-POSIX format (e.g. "/foo/bar") vs
Windows native format that might include a drive letter ("c:\foo\bar").
This breaks the crash_dump decoder, because it tries to split addr2line
output that looks like "filename:linenumber" at the first ':', resulting
in file "c" and line "\foo\bar.c:23" instead of file "c:\foo\bar.c" and
line "23".  It's easily fixed simply by splitting that output at the
last ':' rather than the first.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3946
TEST= trybots + local test on Windows run_untrusted_crash_dump_test_irt nacl_clang=1
R=bradnelson@chromium.org, dschuff@chromium.org, bradnelson@google.com

Review URL: https://codereview.chromium.org/1268603002 .

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client