[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)))) &
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```