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, 6 deletions

diff --git a/Source/cmGetDirectoryPropertyCommand.cxx b/Source/cmGetDirectoryPropertyCommand.cxx
index a92eb71..98ccb0a 100644
--- a/Source/cmGetDirectoryPropertyCommand.cxx
+++ b/Source/cmGetDirectoryPropertyCommand.cxx
@@ -66,7 +66,7 @@ bool cmGetDirectoryPropertyCommand::InitialPass(
       return false;
     }
     std::string const& output = dir->GetSafeDefinition(*i);
-    this->Makefile->AddDefinition(variable, output.c_str());
+    this->Makefile->AddDefinition(variable, output);
     return true;
   }
 
@@ -97,9 +97,5 @@ bool cmGetDirectoryPropertyCommand::InitialPass(
 void cmGetDirectoryPropertyCommand::StoreResult(std::string const& variable,
                                                 const char* prop)
 {
-  if (prop) {
-    this->Makefile->AddDefinition(variable, prop);
-    return;
-  }
-  this->Makefile->AddDefinition(variable, "");
+  this->Makefile->AddDefinition(variable, prop ? prop : "");
 }