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, 3 insertions, 3 deletions

diff --git a/Source/cmGlobalMSYSMakefileGenerator.cxx b/Source/cmGlobalMSYSMakefileGenerator.cxx
index 7b58389..483d4ab 100644
--- a/Source/cmGlobalMSYSMakefileGenerator.cxx
+++ b/Source/cmGlobalMSYSMakefileGenerator.cxx
@@ -69,9 +69,9 @@ void cmGlobalMSYSMakefileGenerator::EnableLanguage(
     rc = trc;
   }
   mf->AddDefinition("MSYS", "1");
-  mf->AddDefinition("CMAKE_GENERATOR_CC", gcc.c_str());
-  mf->AddDefinition("CMAKE_GENERATOR_CXX", gxx.c_str());
-  mf->AddDefinition("CMAKE_GENERATOR_RC", rc.c_str());
+  mf->AddDefinition("CMAKE_GENERATOR_CC", gcc);
+  mf->AddDefinition("CMAKE_GENERATOR_CXX", gxx);
+  mf->AddDefinition("CMAKE_GENERATOR_RC", rc);
   this->cmGlobalUnixMakefileGenerator3::EnableLanguage(l, mf, optional);
 
   if (!mf->IsSet("CMAKE_AR") && !this->CMakeInstance->GetIsInTryCompile() &&