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, 1 insertions, 5 deletions

diff --git a/Source/cmMakefileTargetGenerator.cxx b/Source/cmMakefileTargetGenerator.cxx
index 408f287..df89275 100644
--- a/Source/cmMakefileTargetGenerator.cxx
+++ b/Source/cmMakefileTargetGenerator.cxx
@@ -245,9 +245,6 @@ std::string cmMakefileTargetGenerator::GetFlags(const std::string &l)
     std::string flags;
     const char *lang = l.c_str();
 
-    bool shared = ((this->Target->GetType() == cmTarget::SHARED_LIBRARY) ||
-                   (this->Target->GetType() == cmTarget::MODULE_LIBRARY));
-
     // Add language feature flags.
     this->AddFeatureFlags(flags, lang);
 
@@ -260,8 +257,7 @@ std::string cmMakefileTargetGenerator::GetFlags(const std::string &l)
       this->AddFortranFlags(flags);
       }
 
-    // Add shared-library flags if needed.
-    this->LocalGenerator->AddSharedFlags(flags, lang, shared);
+    this->LocalGenerator->AddCMP0018Flags(flags, this->Target, lang);
 
     // Add include directory flags.
     this->AddIncludeFlags(flags, lang);