add_library: Restore error on alias of non-global imported target

In commit v3.11.0-rc1~433^2~1 (Add support for IMPORTED GLOBAL targets
to be aliased, 2017-09-14) we accidentally dropped the error on calling
`add_library` to alias an imported target that is not globally visible.
The `add_executable` command's equivalent check was properly updated.
Restore the check in `add_library` with the same update.  Also fix the
test case accordingly.

Fixes: #17982

Help/release/3.11.rst

@@ -283,3 +283,12 @@ Changes made since CMake 3.11.0 include the following.
   CMake 3.11.0.  This has been reverted due to changing behavior of
   checks for existing projects.  It may be restored in the future
   with a policy for compatibility.
+
+3.11.2
+------
+
+* Calling :command:`add_library` to create an alias of an imported
+  target that is not globally visible now causes an error again as
+  it did prior to 3.11.0.  This diagnostic was accidentally dropped
+  from CMake 3.11.0 and 3.11.1 by the change to allow globally visible
+  imported targets to be aliased.

Source/cmAddLibraryCommand.cxx

@@ -228,6 +228,14 @@ bool cmAddLibraryCommand::InitialPass(std::vector<std::string> const& args,
       this->SetError(e.str());
       return false;
     }
+    if (aliasedTarget->IsImported() &&
+        !aliasedTarget->IsImportedGloballyVisible()) {
+      std::ostringstream e;
+      e << "cannot create ALIAS target \"" << libName << "\" because target \""
+        << aliasedName << "\" is imported but not globally visible.";
+      this->SetError(e.str());
+      return false;
+    }
     this->Makefile->AddAlias(libName, aliasedName);
     return true;
   }

Tests/RunCMake/alias_targets/imported-target-stderr.txt

@@ -3,7 +3,13 @@
   \"test-exe\" is imported but not globally visible.
 Call Stack \(most recent call first\):
   CMakeLists.txt:[0-9]+ \(include\)
-
-
++
 'alias-test-exe' does not exist![?]
+*
+CMake Error at imported-target.cmake:[0-9]+ \(add_library\):
+  add_library cannot create ALIAS target "alias-test-lib" because target
+  "test-lib" is imported but not globally visible.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:[0-9]+ \(include\)
++
 'alias-test-lib' does not exist![?]$