Make CrashInfo a POD type.

There is no reason to use inheritence for the structures, simply
put them all in the structure properly. The trick is that the
CrashInfoDynamic part will not be filled in for crashes on static
executables.

Rename the CrashInfoDataStatic to CrashInfoDataCommon since it is common
in all crashes.

Add comments and extra static_asserts to verify that CrashInfo is set
up properly.

This also fixes a number of warnings related to offsetof being
used on a non-POD type.

Test: Builds without warnings.
Test: All unit tests pass.
Test: Ran crasher/crasher64 and verified tombstones are correct.
Test: Ran static_crashser/static_crasher64 and verified tombstones are correct.
Change-Id: Ie037d53d1fb505dcdbd2747956979501b17aebab