Mac 10.6 SDK compatibility

Mac 10.6 SDK compatibility.

A couple of the problems related to not having a C++11 library:

 - You can’t put const elements into a std::vector<>, so
   CrashReportDatabase::GetPendingReports() and
   CrashReportDatabase::GetCompletedReports() need to change. There was
   no data-safety benefit to const elements.
 - std::string::pop_back() does not exist, another mechanism must be
   used to trim strings in BreakpadHTTPFormParametersFromMinidump().

One relates to a feature that does not exist in 10.6:

 - The O_CLOEXEC flag to open() was introduced in 10.7. Although it
   would be possible to use fcntl(..., F_SETFD, FD_CLOEXEC) on 10.6, the
   O_CLOEXEC behavior is just removed from
   CrashReportDatabaseMac::ObtainReportLock(), in line with other open()
   calls in Crashpad.

And one was a real bug:

 - #define __STDC_FORMAT_MACROS before #including <inttypes.h> to get
   format macros like SCNx32, used in UUID::InitializeFromString().

TEST=* (gyp_crashpad.py -Dmac_sdk=10.6 -Dmac_deployment_target=10.6)
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/79177046d33a7e5a7da776631a8bf14261d29804

[Mark Mentovai, 2015-03-06 19:59:52]

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

[Robert Sesek, 2015-03-06 21:10:12]

LGTM

[Mark Mentovai, 2015-03-06 23:43:32]

Committed patchset #2 (id:20001) manually as
79177046d33a7e5a7da776631a8bf14261d29804 (presubmit successful).