Make printf warnings refer to intmax_t et al. by name

Make printf warnings refer to intmax_t et al. by name
in addition to underlying type.

For example, the warning for printf("%zu", 42.0);
changes from "conversion specifies type 'unsigned long'" to "conversion
specifies type 'size_t' (aka 'unsigned long')"

(This is a second attempt after r145697, which got reverted.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@146032 91177308-0d34-0410-b5e6-96231b3b80d8