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, 2 insertions, 2 deletions

diff --git a/Source/cmGlobalXCodeGenerator.cxx b/Source/cmGlobalXCodeGenerator.cxx
index 522f3da..938977b 100644
--- a/Source/cmGlobalXCodeGenerator.cxx
+++ b/Source/cmGlobalXCodeGenerator.cxx
@@ -1594,14 +1594,14 @@ void cmGlobalXCodeGenerator::CreateBuildSettings(cmTarget& target,
     if(strcmp(lang, "CXX") == 0)
       {
       this->CurrentLocalGenerator->AddLanguageFlags(cflags, "C", configName);
-      this->CurrentLocalGenerator->AddSharedFlags(cflags, lang, shared);
+      this->CurrentLocalGenerator->AddCMP0018Flags(cflags, &target, "C");
       }
 
     // Add language-specific flags.
     this->CurrentLocalGenerator->AddLanguageFlags(flags, lang, configName);
 
     // Add shared-library flags if needed.
-    this->CurrentLocalGenerator->AddSharedFlags(flags, lang, shared);
+    this->CurrentLocalGenerator->AddCMP0018Flags(flags, &target, lang);
     }
   else if(binary)
   {