This replaces invocations of
- `cmSystemTools::IsInternallyOn` with `cmIsInternallyOn`
- `cmSystemTools::IsNOTFOUND` with `cmIsNOTFOUND`
- `cmSystemTools::IsOn` with `cmIsOn`
- `cmSystemTools::IsOff` with `cmIsOff`
This changes `cmMakefile::AddDefinition` to take a `cm::string_view` as value
argument instead of a `const char *`.
Benefits are:
- `std::string` can be passed to `cmMakefile::AddDefinition` directly without
the `c_str()` plus string length recomputation fallback.
- Lengths of literals passed to `cmMakefile::AddDefinition` can be computed at
compile time.
In various sources uses of `cmMakefile::AddDefinition` are adapted to avoid
`std::string::c_str` calls and the `std::string` is passed directly.
Uses of `cmMakefile::AddDefinition`, where a `nullptr` `const char*` might
be passed to `cmMakefile::AddDefinition` are extended with `nullptr` checks.
Sebastian Holtermann