[clang] [Clang] Fix warning for non std functions with name `infinity` (PR #123417)

[Shafik Yaghmour via cfe-commits]

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@@ -216,11 +244,18 @@ int compareit(float a, float b) {
 
 // no-inf-no-nan-warning at +2 {{use of infinity is undefined behavior due to the currently enabled floating-point options}}
 // no-inf-warning at +1 {{use of infinity is undefined behavior due to the currently enabled floating-point options}}
-  double y = i * numeric_limits<double>::infinity();
+  double y = i * std::numeric_limits<double>::infinity();
+
+  y = i * numeric_limits<double>::infinity(); // expected-no-diagnostics
 
 // no-inf-no-nan-warning at +2 {{use of infinity is undefined behavior due to the currently enabled floating-point options}}
 // no-inf-warning at +1 {{use of infinity is undefined behavior due to the currently enabled floating-point options}}
-  j = numeric_limits<float>::infinity();
+  j = std::numeric_limits<float>::infinity();
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shafik wrote:

So what happens if we are using `using namespace std` and use `numeric_limits<...>::infinity()` do we expect a diagnostic?

https://github.com/llvm/llvm-project/pull/123417