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, 2 deletions

diff --git a/Source/cmCMakeMinimumRequired.cxx b/Source/cmCMakeMinimumRequired.cxx
index 4b4bca2436..f2eae38b8d 100644
--- a/Source/cmCMakeMinimumRequired.cxx
+++ b/Source/cmCMakeMinimumRequired.cxx
@@ -61,8 +61,7 @@ bool cmCMakeMinimumRequired::InitialPass(std::vector<std::string> const& args,
   }
 
   // Save the required version string.
-  this->Makefile->AddDefinition("CMAKE_MINIMUM_REQUIRED_VERSION",
-                                version_min.c_str());
+  this->Makefile->AddDefinition("CMAKE_MINIMUM_REQUIRED_VERSION", version_min);
 
   // Get the current version number.
   unsigned int current_major = cmVersion::GetMajorVersion();