BUG: Recognize .so shared libraries on HP-UX

HP-UX uses both .sl and .so as extensions for shared libraries.  This
teaches CMake to recognize .so shared libraries so they are treated
properly during link dependency analysis.

Modules/Platform/HP-UX.cmake

@@ -1,6 +1,7 @@
 SET(CMAKE_SHARED_LIBRARY_SUFFIX ".sl")          # .so
 SET(CMAKE_DL_LIBS "dld")
 SET(CMAKE_FIND_LIBRARY_SUFFIXES ".sl" ".so" ".a")
+SET(CMAKE_EXTRA_SHARED_LIBRARY_SUFFIXES ".so")
 
 # The HP linker needs to find transitive shared library dependencies
 # in the -L path.  Therefore the runtime path must be added to the

Source/cmComputeLinkInformation.cxx

@@ -814,6 +814,17 @@ void cmComputeLinkInformation::ComputeItemParserInfo()
       this->AddLinkExtension(i->c_str(), LinkUnknown);
       }
     }
+  if(const char* sharedSuffixes =
+     mf->GetDefinition("CMAKE_EXTRA_SHARED_LIBRARY_SUFFIXES"))
+    {
+    std::vector<std::string> sharedSuffixVec;
+    cmSystemTools::ExpandListArgument(sharedSuffixes, sharedSuffixVec);
+    for(std::vector<std::string>::iterator i = sharedSuffixVec.begin();
+        i != sharedSuffixVec.end(); ++i)
+      {
+      this->AddLinkExtension(i->c_str(), LinkShared);
+      }
+    }
 
   // Compute a regex to match link extensions.
   std::string libext = this->CreateExtensionRegex(this->LinkExtensions);

Source/cmDocumentVariables.cxx

@@ -377,6 +377,15 @@ void cmDocumentVariables::DefineVariables(cmake* cm)
      "The suffix to use for the end of a static library, .lib on Windows.",
      false,
      "Variables that Provide Information");
+  cm->DefineProperty
+    ("CMAKE_EXTRA_SHARED_LIBRARY_SUFFIXES", cmProperty::VARIABLE,
+     "Additional suffixes for shared libraries.",
+     "Extensions for shared libraries other than that specified by "
+     "CMAKE_SHARED_LIBRARY_SUFFIX, if any.  "
+     "CMake uses this to recognize external shared library files during "
+     "analysis of libraries linked by a target.",
+     false,
+     "Variables that Provide Information");
 
 
   // Variables defined by cmake, that change the behavior