cmInstallCommand: tweak error message

Not all filesets need to be installed; just those that are visible on
the target's interface. Clarify the error message.

Source/cmInstallCommand.cxx

@@ -741,9 +741,9 @@ bool HandleTargetsMode(std::vector<std::string> const& args,
                   [=](const cmInstallCommandFileSetArguments& fileSetArg)
                     -> bool { return fileSetArg.GetFileSet() == name; });
               })) {
-          status.SetError(cmStrCat(
-            "TARGETS target ", target.GetName(),
-            " is exported but not all of its file sets are installed"));
+          status.SetError(cmStrCat("TARGETS target ", target.GetName(),
+                                   " is exported but not all of its interface "
+                                   "file sets are installed"));
           return false;
         }
 

Tests/RunCMake/target_sources/FileSetInstallMissingSetsInterface-stderr.txt

@@ -1,5 +1,5 @@
 ^CMake Error at FileSetInstallMissingSetsInterface\.cmake:[0-9]+ \(install\):
-  install TARGETS target lib1 is exported but not all of its file sets are
-  installed
+  install TARGETS target lib1 is exported but not all of its interface file
+  sets are installed
 Call Stack \(most recent call first\):
   CMakeLists\.txt:[0-9]+ \(include\)$