Add new warning for compound punctuation tokens that are split across macro expansions or split by whitespace.
For example:
#define FOO(x) (x)
FOO({});
... forms a statement-expression after macro expansion. This warning
applies to '({' and '})' delimiting statement-expressions, '[[' and ']]'
delimiting attributes, and '::*' introducing a pointer-to-member.
The warning for forming these compound tokens across macro expansions
(or across files!) is enabled by default; the warning for whitespace
within the tokens is not, but is included in -Wall.
Differential Revision: https://reviews.llvm.org/D86751