[analyzer] Look through SubstNonTypeTemplateParmExprs.

We were treating this like a CXXDefaultArgExpr, but
SubstNonTypeTemplateParmExpr actually appears when a template is
instantiated, i.e. we have all the information necessary to evaluate it.
This allows us to inline functions like llvm::array_lengthof.

<rdar://problem/11949235>

llvm-svn: 160846