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/cmGetTargetPropertyCommand.cxx b/Source/cmGetTargetPropertyCommand.cxx
index fc0e9c6..07aaf02 100644
--- a/Source/cmGetTargetPropertyCommand.cxx
+++ b/Source/cmGetTargetPropertyCommand.cxx
@@ -75,9 +75,9 @@ bool cmGetTargetPropertyCommand::InitialPass(
     }
   }
   if (prop_exists) {
-    this->Makefile->AddDefinition(var, prop.c_str());
+    this->Makefile->AddDefinition(var, prop);
     return true;
   }
-  this->Makefile->AddDefinition(var, (var + "-NOTFOUND").c_str());
+  this->Makefile->AddDefinition(var, var + "-NOTFOUND");
   return true;
 }