Add the ability to defer the initialization of the SyzyAsan crash reporter.

This CL adds a new flag to the SYZYASAN_RTL_OPTIONS (which can also be set at
instrumentation time) to delay the initialization of the crash reporter. By
default the runtime try to initialize its crash reporter (e.g. connecting to the
Crashpad one) during its initialization (i.e. when the SyzyAsan runtime get
loaded), but in some cases this can fail because the crash reporter that we try
to connect to isn't ready yet. This function adds a new function that the
instrumented process can call once it has initialized his crash reporter.

We don't need this for Chrome because by the time we load the instrumented
chrome.dll (which loads syzyasan_rtl.dll) we know that the Crashpad reporter has
been initialized so we can connect to it directly, but this doesn't work when
instrumenting a .exe file, so if it want to use the advanced crash reporting it'll
need to use this new flag at compile time and to manually call the
asan_InitializeCrashHandler function once its crash reporter is ready.

* By 'crash reporter' I mean Crashpad.

BUG=chromium:557759

Review-Url: https://codereview.chromium.org/2576003002