Improved test coverage of MathLib.
#6306 false positive with strxfrm NULL argument. Adjust std.cfg in favor of no false positive
#6301 Unused shared lock variable. Add exception for std::shared_lock() to CheckUnusedVar::checkFunctionVariableUsage_iterateScopes()
Make expensive string manipulation depend on settings
Merge pull request #477 from orbitcowboy/master

Improved test coverage of MathLib.
Remove dead code in CheckMemoryLeakInFunction::call_func() (Coverity CID 1257017)
Fixed #6308: Properly associate Function with Scope for destructors in SymbolDatabase
Fixed #6291 and #6293: Support :: in front of function name in checkUnusedFunctions

Simplified code in CheckUnusedFunctions
Fixed a couple of #6276 integer over/underflow issues
Fixed #6266: Support noexcept(false)
Fixed wrong configuration of modf in std.cfg (#6312)
posix.cfg: Added support for readdir().
Fixed false positives about strdupa() / strndupa() memleak

strdupa() / strndupa() allocates memory on the stack using alloca().
This memory is freed automatically once the current function is left.