Revise implementation of case-insensitive command names

Store both the as-written and lower-case command names and use
the latter to avoid case-insensitive string comparisons.

With this I obtain 2-6% speed increase (on Windows) for the configure
step with no significant changes in memory usage.  A case-insensitive
comparison is a lot slower than just calling `==` because the operator
will use things like memcmp, so prefer the latter.

The `cmSystemTools::LowerCase` function allocates a new string each time
it is called, so before this change we were allocating in:

* cmMakefile::Configure two times for each function
  (to look for `cmake_minimum_required` and `project`)
* cmMakefile::ExecuteCommand twice by function by calling
  cmState::GetCommand and copying the name

Now we are only allocating once by function instead of four.

1 files changed, 4 insertions, 0 deletions

diff --git a/Source/cmState.h b/Source/cmState.h
index 4c6fc69..38bdfec 100644
--- a/Source/cmState.h
+++ b/Source/cmState.h
@@ -125,7 +125,11 @@ public:
   bool GetIsGeneratorMultiConfig() const;
   void SetIsGeneratorMultiConfig(bool b);
 
+  // Returns a command from its name, case insensitive, or nullptr
   cmCommand* GetCommand(std::string const& name) const;
+  // Returns a command from its name, or nullptr
+  cmCommand* GetCommandByExactName(std::string const& name) const;
+
   void AddBuiltinCommand(std::string const& name, cmCommand* command);
   void AddDisallowedCommand(std::string const& name, cmCommand* command,
                             cmPolicies::PolicyID policy, const char* message);