VS: Do not accumulate configurations globally (#15577)

Drop the VS >= 7 generator's global Configurations member and instead
lookup configurations using cmMakefile::GetConfigurations where needed.
This avoids accumulating all CMAKE_CONFIGURATION_TYPES values ever
encountered by a project() or enable_language() command and allows
the final value to be used in each directory.  We don't officially
support per-directory CMAKE_CONFIGURATION_TYPES values but we certainly
should not generate configurations not in the final value in the top
level directory.

Source/cmLocalVisualStudio7Generator.h

@@ -77,6 +77,7 @@ private:
   void WriteVCProjFile(std::ostream& fout, const std::string& libName,
                        cmTarget &tgt);
   void WriteConfigurations(std::ostream& fout,
+                           std::vector<std::string> const& configs,
                            const std::string& libName, cmTarget &tgt);
   void WriteConfiguration(std::ostream& fout,
                           const std::string& configName,
@@ -101,6 +102,7 @@ private:
   void WriteVCProjEndGroup(std::ostream& fout);
 
   void WriteCustomRule(std::ostream& fout,
+                       std::vector<std::string> const& configs,
                        const char* source,
                        const cmCustomCommand& command,
                        FCInfo& fcinfo);
@@ -109,7 +111,7 @@ private:
   bool WriteGroup(const cmSourceGroup *sg,
                   cmTarget& target, std::ostream &fout,
                   const std::string& libName,
-                  std::vector<std::string> *configs);
+                  std::vector<std::string> const& configs);
 
   friend class cmLocalVisualStudio7GeneratorFCInfo;
   friend class cmLocalVisualStudio7GeneratorInternals;