[clang][SourceManager] Fix -Wparentheses warning (NFC)

GCC warning:
```
/llvm-project/clang/lib/Basic/SourceManager.cpp: In instantiation of ‘constexpr T likelyhasbetween(T, unsigned char, unsigned char) [with T = long unsigned int]’:
/llvm-project/clang/lib/Basic/SourceManager.cpp:1292:52:   required from here
/llvm-project/clang/lib/Basic/SourceManager.cpp:1264:48: warning: suggest parentheses around ‘+’ in operand of ‘&’ [-Wparentheses]
 1264 |           (x & ~static_cast<T>(0) / 255 * 127) +
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
 1265 |               (~static_cast<T>(0) / 255 * (127 - (m - 1)))) &
      |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```