Skip file-level dependencies on custom targets (#11332)

A custom command may name a target created by add_custom_target in its
DEPENDS field.  Treat this case as a target-level dependency only since
a custom target provides no standard file on which to add a file-level
dependency.

Source/cmLocalGenerator.cxx

@@ -1878,10 +1878,9 @@ bool cmLocalGenerator::GetRealDependency(const char* inName,
         break;
       case cmTarget::UTILITY:
       case cmTarget::GLOBAL_TARGET:
-        // Depending on a utility target may not work but just trust
-        // the user to have given a valid name.
-        dep = inName;
-        return true;
+        // A utility target has no file on which to depend.  This was listed
+        // only to get the target-level dependency.
+        return false;
       case cmTarget::INSTALL_FILES:
       case cmTarget::INSTALL_PROGRAMS:
       case cmTarget::INSTALL_DIRECTORY:

Source/cmLocalGenerator.h

@@ -158,6 +158,7 @@ public:
 
   /** Translate a dependency as given in CMake code to the name to
       appear in a generated build file.  If the given name is that of
+      a utility target, returns false.  If the given name is that of
       a CMake target it will be transformed to the real output
       location of that target for the given configuration.  If the
       given name is the full path to a file it will be returned.

Tests/CustomCommand/CMakeLists.txt

@@ -130,6 +130,7 @@ ADD_CUSTOM_COMMAND(
 ################################################################
 ADD_CUSTOM_COMMAND(OUTPUT ${PROJECT_BINARY_DIR}/foo.pre
   DEPENDS ${PROJECT_SOURCE_DIR}/foo.in
+          TDocument # Ensure doc1.h generates before this target
   COMMAND   ${CMAKE_COMMAND}  
   ARGS      -E copy ${PROJECT_SOURCE_DIR}/foo.in 
   ${PROJECT_BINARY_DIR}/foo.pre
@@ -181,10 +182,6 @@ ADD_CUSTOM_COMMAND(OUTPUT ${PROJECT_BINARY_DIR}/generated.c
 
 TARGET_LINK_LIBRARIES(CustomCommand GeneratedHeader)
 
-# must add a dependency on TDocument otherwise it might never build and 
-# the CustomCommand executable really needs doc1.h
-ADD_DEPENDENCIES(CustomCommand TDocument)
-
 ##############################################################################
 # Test for using just the target name as executable in the COMMAND
 # section. Has to be recognized and replaced by CMake with the output