Give Type::isIntegralType() an ASTContext parameter, so that it

Give Type::isIntegralType() an ASTContext parameter, so that it
provides C "integer type" semantics in C and C++ "integral type"
semantics in C++.

Note that I still need to update isIntegerType (and possibly other
predicates) using the same approach I've taken for
isIntegralType(). The two should have the same meaning, but currently
don't (!).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@106074 91177308-0d34-0410-b5e6-96231b3b80d8