[clang] [analyzer] Fix FP for cplusplus.placement new #149240 (PR #150161)

[Donát Nagy via cfe-commits]

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@@ -168,8 +168,8 @@ void f1() {
 
   // bad (not enough space).
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NagyDonat wrote:

If you change the behavior of this checker in this situation, then please update this comment and explain that the code of the test would be problematic on systems where placement array new allocates more memory than the size of the array, but the checker doesn't report this because hopefully this is rare. 

https://github.com/llvm/llvm-project/pull/150161