Fix a few cases where enum constant handling was using

ASTContext::getTypeSize() rather than ASTContext::getIntWidth() for
the width of an integral type. The former includes padding for bools
(to the target's size) while the latter does not, so we woud end up
zero-extending bools to the target width when we shouldn't. Fixes a
crash-on-valid in the included test.

llvm-svn: 101372