Refactor generation of shared library flags

CMAKE_SHARED_LIBRARY_<lang>_FLAGS has flags on various platforms for a
variety of purposes that are correlated with shared libraries but not
exclusive to them.  Refactor generation of these flags to use new
purpose-specific platform variables

  CMAKE_<lang>_COMPILE_OPTIONS_DLL
  CMAKE_<lang>_COMPILE_OPTIONS_PIC
  CMAKE_<lang>_COMPILE_OPTIONS_PIE

Activate the DLL flags specifically for shared libraries.  Add a new
POSITION_INDEPENDENT_CODE target property to activate PIC/PIE flags, and
default to true for shared libraries to preserve default behavior.
Initialize the new property from CMAKE_POSITION_INDEPENDENT_CODE to
allow easy global configuration in projects.

Although the default behavior is unchanged by this refactoring, the new
approach ignores CMAKE_SHARED_LIBRARY_<lang>_FLAGS completely.  We must
leave it set in case projects reference the value.  Furthermore, if a
project modifies CMAKE_SHARED_LIBRARY_<lang>_FLAGS it expects the new
value to be used.  Add policy CMP0018 to handle compatibility with
projects that modify this platform variable.

Add a PositionIndependentCode test on platforms where we can get
meaningful results.

1 files changed, 7 insertions, 1 deletions

diff --git a/Source/cmLocalGenerator.h b/Source/cmLocalGenerator.h
index cb84a30..1d8a7d1 100644
--- a/Source/cmLocalGenerator.h
+++ b/Source/cmLocalGenerator.h
@@ -140,7 +140,8 @@ public:
 
   void AddLanguageFlags(std::string& flags, const char* lang,
                         const char* config);
-  void AddSharedFlags(std::string& flags, const char* lang, bool shared);
+  void AddCMP0018Flags(std::string &flags, cmTarget* target,
+                       std::string const& lang);
   void AddConfigVariableFlags(std::string& flags, const char* var,
                               const char* config);
   ///! Append flags to a string.
@@ -425,6 +426,11 @@ protected:
 private:
   std::string ConvertToOutputForExistingCommon(const char* remote,
                                                std::string const& result);
+
+  void AddSharedFlags(std::string& flags, const char* lang, bool shared);
+  bool GetShouldUseOldFlags(bool shared, const std::string &lang) const;
+  void AddPositionIndependentFlags(std::string& flags, std::string const& l,
+                                   int targetType);
 };
 
 #endif