The Syntax enumeration requires at least three bits to store all of its values. Increase the number of bits for SyntaxUsed. Decrease the number of expression arguments allowed by a single bit so that the bit fields continue to add up to 32-bits evenly.

There is no test for this fix because I could find no reasonable way to trigger a visible failure from it.

Thanks to Doug Gregor for spotting this!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@222456 91177308-0d34-0410-b5e6-96231b3b80d8