BT<> and cmLocalGenerator: Add helpers functions

* Template remove_BT<> to extract content from BT wrapper
* cmLocalGenerator::AppendDefines which take std::set<> and std::vector<BT<>> as arguments

Source/cmListFileCache.h

@@ -6,12 +6,14 @@
 
 #include <iosfwd>
 #include <memory>
+#include <set>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include <cm/optional>
 #include <cm/string_view>
+#include <cmext/type_traits>
 
 #include "cmList.h"
 #include "cmStack.h"
@@ -206,6 +208,36 @@ public:
 
 std::ostream& operator<<(std::ostream& os, BT<std::string> const& s);
 
+namespace cm {
+// Helpers for basic type retrieval
+template <typename T>
+T remove_BT(BT<T> const& bt)
+{
+  return bt.Value;
+}
+
+template <typename T>
+std::vector<T> remove_BT(std::vector<BT<T>> const& container)
+{
+  std::vector<T> result;
+  for (auto const& entry : container) {
+    result.emplace_back(entry.Value);
+  }
+
+  return result;
+}
+template <typename T>
+std::set<T> remove_BT(std::set<BT<T>> const& container)
+{
+  std::set<T> result;
+  for (auto const& entry : container) {
+    result.emplace(entry.Value);
+  }
+
+  return result;
+}
+}
+
 // Wrap type T as a value with potentially multiple backtraces.  For purposes
 // of ordering and equality comparison, only the original value is used.  The
 // backtrace is considered incidental.

Source/cmLocalGenerator.cxx

@@ -3914,6 +3914,17 @@ void cmLocalGenerator::AppendDefines(std::set<std::string>& defines,
   }
 }
 
+void cmLocalGenerator::AppendDefines(
+  std::set<std::string>& defines,
+  std::vector<BT<std::string>> const& defines_vec) const
+{
+  std::set<BT<std::string>> tmp;
+  this->AppendDefines(tmp, defines_vec);
+  for (BT<std::string> const& i : tmp) {
+    defines.emplace(i.Value);
+  }
+}
+
 void cmLocalGenerator::AppendDefines(std::set<BT<std::string>>& defines,
                                      std::string const& defines_list) const
 {

Source/cmLocalGenerator.h

@@ -266,6 +266,8 @@ public:
    */
   void AppendDefines(std::set<std::string>& defines,
                      std::string const& defines_list) const;
+  void AppendDefines(std::set<std::string>& defines,
+                     std::vector<BT<std::string>> const& defines_vec) const;
   void AppendDefines(std::set<BT<std::string>>& defines,
                      std::string const& defines_list) const;
   void AppendDefines(std::set<BT<std::string>>& defines,