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, 1 deletions

diff --git a/Source/cmLoadCacheCommand.cxx b/Source/cmLoadCacheCommand.cxx
index b1fee8d..3fd7343 100644
--- a/Source/cmLoadCacheCommand.cxx
+++ b/Source/cmLoadCacheCommand.cxx
@@ -153,7 +153,7 @@ void cmLoadCacheCommand::CheckLine(const char* line)
       // prefix.
       var = this->Prefix + var;
       if (!value.empty()) {
-        this->Makefile->AddDefinition(var, value.c_str());
+        this->Makefile->AddDefinition(var, value);
       } else {
         this->Makefile->RemoveDefinition(var);
       }