Honor $<LINK_ONLY> when checking interface properties

Callers of cmTarget::GetLinkImplementationClosure are interested in the
set of targets whose interface properties propagate to the current
target.  This excludes targets guarded by $<LINK_ONLY>.

Teach the CompatibleInterface test to cover suppression of interface
compatibility tests with $<LINK_ONLY>.  Although this is not recommended
in practice, it is a way of covering the above behavior.

Source/cmTarget.cxx

@@ -6018,7 +6018,7 @@ void processILibs(const std::string& config,
     {
     tgts.push_back(item.Target);
     if(cmTarget::LinkInterface const* iface =
-       item.Target->GetLinkInterfaceLibraries(config, headTarget, false))
+       item.Target->GetLinkInterfaceLibraries(config, headTarget, true))
       {
       for(std::vector<cmLinkItem>::const_iterator
             it = iface->Libraries.begin();

Tests/CompatibleInterface/CMakeLists.txt

@@ -1,5 +1,5 @@
 
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 3.0)
 
 project(CompatibleInterface)
 
@@ -54,6 +54,15 @@ set_property(TARGET iface1 PROPERTY INTERFACE_NUMBER_MAX_PROP2 200)
 add_executable(CompatibleInterface main.cpp)
 target_link_libraries(CompatibleInterface iface1)
 
+add_library(foo STATIC foo.cpp)
+add_library(bar SHARED bar.cpp)
+set_property(TARGET foo APPEND PROPERTY COMPATIBLE_INTERFACE_BOOL SOMEPROP)
+set_property(TARGET foo PROPERTY INTERFACE_SOMEPROP ON)
+# Use LINK_ONLY to suppress usage requirements and allow the check to pass.
+set_property(TARGET bar PROPERTY INTERFACE_LINK_LIBRARIES $<LINK_ONLY:foo>)
+set_property(TARGET CompatibleInterface PROPERTY SOMEPROP OFF)
+target_link_libraries(CompatibleInterface bar)
+
 set_property(TARGET CompatibleInterface PROPERTY BOOL_PROP2 ON)
 set_property(TARGET CompatibleInterface PROPERTY BOOL_PROP3 ON)
 set_property(TARGET CompatibleInterface PROPERTY STRING_PROP2 prop2)

Tests/CompatibleInterface/bar.cpp

@@ -0,0 +1,7 @@
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+int bar()
+{
+  return 0;
+}

Tests/CompatibleInterface/foo.cpp

@@ -0,0 +1,4 @@
+int foo()
+{
+  return 0;
+}

Tests/CompatibleInterface/main.cpp

@@ -40,8 +40,14 @@ enum {
 
 #include "iface2.h"
 
+int foo();
+#ifdef _WIN32
+__declspec(dllimport)
+#endif
+int bar();
+
 int main(int argc, char **argv)
 {
   Iface2 if2;
-  return if2.foo();
+  return if2.foo() + foo() + bar();
 }