Get rid of SanitizerOptions::Disabled global. NFC.

SanitizerOptions is not even a POD now, so having global variable of
this type, is not nice. Instead, provide a regular constructor and clear()
method, and let each CodeGenFunction has its own copy of SanitizerOptions
it uses.


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@220920 91177308-0d34-0410-b5e6-96231b3b80d8