-fsanitize=function: fix MSVC hashing to sugared type (#66816)

Hashing the sugared type instead of the canonical type meant that
a simple example like this would always fail under MSVC:

```
static auto l() {}
int main() {
  auto a = l;
  a();
}
```
`clang --target=x86_64-pc-windows-msvc -fno-exceptions
-fsanitize=function -g -O0 -fuse-ld=lld -o test.exe test.cc`

produces:
```
test.cc:4:3: runtime error: call to function l through pointer to incorrect function type 'void (*)()'
```