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, 3 deletions

diff --git a/Source/cmGlobalGenerator.cxx b/Source/cmGlobalGenerator.cxx
index baa8559..7b8ffc5 100644
--- a/Source/cmGlobalGenerator.cxx
+++ b/Source/cmGlobalGenerator.cxx
@@ -525,7 +525,7 @@ void cmGlobalGenerator::EnableLanguage(
   rootBin += cmVersion::GetCMakeVersion();
 
   // set the dir for parent files so they can be used by modules
-  mf->AddDefinition("CMAKE_PLATFORM_INFO_DIR", rootBin.c_str());
+  mf->AddDefinition("CMAKE_PLATFORM_INFO_DIR", rootBin);
 
   if (!this->CMakeInstance->GetIsInTryCompile()) {
     // Keep a mark in the cache to indicate that we've initialized the
@@ -585,8 +585,7 @@ void cmGlobalGenerator::EnableLanguage(
     windowsVersionString << osviex.dwMajorVersion << "."
                          << osviex.dwMinorVersion << "."
                          << osviex.dwBuildNumber;
-    mf->AddDefinition("CMAKE_HOST_SYSTEM_VERSION",
-                      windowsVersionString.str().c_str());
+    mf->AddDefinition("CMAKE_HOST_SYSTEM_VERSION", windowsVersionString.str());
 #endif
     // Read the DetermineSystem file
     std::string systemFile = mf->GetModulesFile("CMakeDetermineSystem.cmake");