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, 1 insertions, 1 deletions

diff --git a/Source/cmExecuteProcessCommand.cxx b/Source/cmExecuteProcessCommand.cxx
index 689fc2023e..8d91f433ca 100644
--- a/Source/cmExecuteProcessCommand.cxx
+++ b/Source/cmExecuteProcessCommand.cxx
@@ -332,7 +332,7 @@ bool cmExecuteProcessCommand::InitialPass(std::vector<std::string> const& args,
           }
         }
         this->Makefile->AddDefinition(arguments.ResultsVariable,
-                                      cmJoin(res, ";").c_str());
+                                      cmJoin(res, ";"));
       } break;
       case cmsysProcess_State_Exception:
         this->Makefile->AddDefinition(arguments.ResultsVariable,