Fix some warnings when compiling crashpad with VC++ 2015 Update 1.
Warning 4302 occurs if you convert from a pointer to a <sizeof(void*)
integer in one cast, because this often indicates an accidental pointer
truncation which can be a bug in 64-bit builds.
Warning 4577 warns that noexcept will not be enforced, but we don't want
it to be enforced anyway, so I disabled it. The full warning is:
warning C4577: 'noexcept' used with no exception handling mode specified
termination on exception is not guaranteed. Specify /EHsc
BUG=440500
R=mark@chromium.org
Review URL: https://codereview.chromium.org/1527803002 .
Patch from Bruce Dawson <brucedawson@chromium.org>.
b0394744cc