Genex: Do not consider 'head' when evaluating build properties

When $<TARGET_PROPERTY> names a build property like COMPILE_DEFINITIONS
but not the usage requirement (INTERFACE_) version of it, the value
should be that used to build the target.  It should not be influenced by
a dependent 'head' target like usage requirements are.

Extend the CompileDefinitions test with a case covering the corrected
behavior.

Reviewed-by: Stephen Kelly <steveire@gmail.com>

Source/cmGeneratorExpressionEvaluator.cxx

@@ -1081,7 +1081,7 @@ static const struct TargetPropertyNode : public cmGeneratorExpressionNode
         }
       }
 #undef POPULATE_INTERFACE_PROPERTY_NAME
-    cmTarget const* headTarget = context->HeadTarget
+    cmTarget const* headTarget = context->HeadTarget && isInterfaceProperty
                                ? context->HeadTarget : target;
 
     if(isInterfaceProperty)
@@ -1103,7 +1103,7 @@ static const struct TargetPropertyNode : public cmGeneratorExpressionNode
         {
         linkedTargetsContent =
           getLinkedTargetsContent(impl->Libraries, target,
-                                  headTarget,
+                                  target,
                                   context, &dagChecker,
                                   interfacePropertyName);
         }

Tests/CompileDefinitions/target_prop/CMakeLists.txt

@@ -53,3 +53,8 @@ set_property(TARGET target_prop_mixed_executable APPEND PROPERTY COMPILE_DEFINIT
     "LINK_LANGUAGE_IS_$<TARGET_PROPERTY:LINKER_LANGUAGE>"
     "C_EXECUTABLE_LINK_LANGUAGE_IS_$<TARGET_PROPERTY:target_prop_c_executable,LINKER_LANGUAGE>"
     )
+
+add_library(tgt STATIC IMPORTED)
+set_property(TARGET tgt APPEND PROPERTY COMPILE_DEFINITIONS TGT_DEF TGT_TYPE_$<TARGET_PROPERTY:TYPE>)
+add_executable(usetgt usetgt.c)
+target_compile_definitions(usetgt PRIVATE $<TARGET_PROPERTY:tgt,COMPILE_DEFINITIONS>)

Tests/CompileDefinitions/target_prop/usetgt.c

@@ -0,0 +1,10 @@
+#ifndef TGT_DEF
+# error TGT_DEF incorrectly not defined
+#endif
+#ifndef TGT_TYPE_STATIC_LIBRARY
+# error TGT_TYPE_STATIC_LIBRARY incorrectly not defined
+#endif
+#ifdef TGT_TYPE_EXECUTABLE
+# error TGT_TYPE_EXECUTABLE incorrectly defined
+#endif
+int main(void) { return 0; }