Fix an "unused variable" compiler warning in exploitability_win.cc

BUG=none
TEST=compile with "-Wall -Werror"

Review URL: https://breakpad.appspot.com/588003

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1171 4c0a9323-5329-0410-9bdc-e9ce6186880e
Add MD_OS_NACL platform_id value for identifying NaCl minidumps

Change minidump-2-core to accept minidumps with this platform_id value
rather than rejecting them as non-Linux dumps.

Add a missing "break" for a MD_OS_PS3 case.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3424
TEST= tested with work-in-progress NaCl minidump generator

Review URL: https://breakpad.appspot.com/590002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1172 4c0a9323-5329-0410-9bdc-e9ce6186880e