diagnose_if fails on constructor templates when the expression is argument-independent

[higher-performance]

This test case for clang/test/SemaCXX/diagnose_if.cpp fails:

struct ConstructorTemplate {
  template <class T>
  explicit ConstructorTemplate(T x)
      _diagnose_if(sizeof(T) == sizeof(char), "oh no", "error") {}
};

void run() {
  ConstructorTemplate('1'); // expected-error{{oh no}}
}

Replacing sizeof(T) with sizeof(x) makes it succeed. It seems the code path for diagnoseArgIndependentDiagnoseIfAttrs isn't called in some cases that it's supposed to, but I got lost trying to track it down.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (higher-performance)

This test case for `clang/test/SemaCXX/diagnose_if.cpp` fails: ``` struct ConstructorTemplate { template <class T> explicit ConstructorTemplate(T x) _diagnose_if(sizeof(T) == sizeof(char), "oh no", "error") {} };

void run() {
ConstructorTemplate('1'); // expected-error{{oh no}}
}

Replacing `sizeof(T)` with `sizeof(x)` makes it succeed. It seems the code path for `diagnoseArgIndependentDiagnoseIfAttrs` isn't called in some cases that it's supposed to, but I got lost trying to track it down.
</details>

[higher-performance]

Thank you!