This patch enhances Clang's diagnosis for unknown attributes by
providing typo correction suggestions for known attributes.
```cpp
[[gmu::deprected]] // expected-warning {{unknown attribute 'gmu::deprected' ignored; did you mean 'gnu::deprecated'?}}
int f1(void) {
return 0;
}
[[deprected]] // expected-warning {{unknown attribute 'deprected' ignored; did you mean 'deprecated'?}}
int f2(void) {
return 0;
}
```
