cmMakefile: Let AddDefinition accept a value as cm::string_view

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.

1 files changed, 2 insertions, 1 deletions

diff --git a/Source/cmFLTKWrapUICommand.cxx b/Source/cmFLTKWrapUICommand.cxx
index 70800b4..b7a2b27 100644
--- a/Source/cmFLTKWrapUICommand.cxx
+++ b/Source/cmFLTKWrapUICommand.cxx
@@ -117,8 +117,9 @@ bool cmFLTKWrapUICommand::InitialPass(std::vector<std::string> const& args,
     }
     sourceListValue += generatedSourcesClasses[classNum]->GetFullPath();
   }
+
   std::string const varName = target + "_FLTK_UI_SRCS";
-  this->Makefile->AddDefinition(varName, sourceListValue.c_str());
+  this->Makefile->AddDefinition(varName, sourceListValue);
 
   this->Makefile->AddFinalAction(
     [target](cmMakefile& makefile) { FinalAction(makefile, target); });