Add the ALIAS target concept for libraries and executables.

* The ALIAS name must match a validity regex.
* Executables and libraries may be aliased.
* An ALIAS acts immutable. It can not be used as the lhs
  of target_link_libraries or other commands.
* An ALIAS can be used with add_custom_command, add_custom_target,
  and add_test in the same way regular targets can.
* The target of an ALIAS can be retrieved with the ALIASED_TARGET
  target property.
* An ALIAS does not appear in the generated buildsystem. It
  is kept separate from cmMakefile::Targets for that reason.
* A target may have multiple aliases.
* An ALIAS target may not itself have an alias.
* An IMPORTED target may not have an alias.
* An ALIAS may not be exported or imported.

1 files changed, 4 insertions, 0 deletions

diff --git a/Tests/RunCMake/alias_targets/imported-stderr.txt b/Tests/RunCMake/alias_targets/imported-stderr.txt
new file mode 100644
index 0000000..b905847
--- /dev/null
+++ b/Tests/RunCMake/alias_targets/imported-stderr.txt
@@ -0,0 +1,4 @@
+CMake Error at imported.cmake:2 \(add_library\):
+  add_library IMPORTED with ALIAS is not allowed.
+Call Stack \(most recent call first\):
+  CMakeLists.txt:3 \(include\)