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, 2 deletions

diff --git a/Source/cmSeparateArgumentsCommand.cxx b/Source/cmSeparateArgumentsCommand.cxx
index 28cbdc0..ab4a0c7 100644
--- a/Source/cmSeparateArgumentsCommand.cxx
+++ b/Source/cmSeparateArgumentsCommand.cxx
@@ -69,7 +69,7 @@ bool cmSeparateArgumentsCommand::InitialPass(
     if (const char* def = this->Makefile->GetDefinition(var)) {
       std::string value = def;
       std::replace(value.begin(), value.end(), ' ', ';');
-      this->Makefile->AddDefinition(var, value.c_str());
+      this->Makefile->AddDefinition(var, value);
     }
   } else {
     // Parse the command line.
@@ -97,7 +97,7 @@ bool cmSeparateArgumentsCommand::InitialPass(
         value += si;
       }
     }
-    this->Makefile->AddDefinition(var, value.c_str());
+    this->Makefile->AddDefinition(var, value);
   }
 
   return true;