[clang] [C2y] Add test coverage for N3298 (PR #112033)

[Erich Keane via cfe-commits]

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@@ -57,7 +57,7 @@ void test4(void) {
 
       var =+5;  // no warning when the subexpr of the unary op has no space before it.
       var =-5;
-  
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erichkeane wrote:

Handful of WS changes in this file, though not sure I care enough to have you change this.

https://github.com/llvm/llvm-project/pull/112033