Make the cwriter use the lowerinvoke pass so that it can either use "disabled exceptions" or

"expensive exceptions" controlled by an option.  Also refactor and eliminate a bunch of cruft.
This is a temporary solution and causes millions of warnings to pour out of programs that use
exceptions, but it should fix the problem with sparc and the 'write' declaration (PR190).
Subsequent changes will make this stink much less

llvm-svn: 11405