Revert "intmax_t is long long on Darwin, not long."

'long' and 'long long' are different for the purposes of mangling.
This caused <rdar://problem/13254874>.

This reverts commit c2f994d31ec85e9af811af38eb1b28709aef0b2c.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175681 91177308-0d34-0410-b5e6-96231b3b80d8