[clang-tidy] Add check 'misc-string-compare'.

I have a created a new check for clang tidy: misc-string-compare. This will check for incorrect usage of std::string::compare when used to check equality or inequality of string instead of the string equality or inequality operators.

Example:
```
  std::string str1, str2;
  if (str1.compare(str2)) {
  }
```

Reviewers: hokein, aaron.ballman, alexfh, malcolm.parsons

Subscribers: xazax.hun, Eugene.Zelenko, cfe-commits, malcolm.parsons, Prazek, mgorny, JDevlieghere

Differential Revision: https://reviews.llvm.org/D27210

llvm-svn: 290747