[PATCH] [libcxxabi] Add lit configs for libcxxabi tests.

[Dan Albert]

================
Comment at: test/CMakeLists.txt:41
@@ +40,3 @@
+      COMMENT "Running libcxxabi tests")
+  else()
+    add_custom_target(check-libcxxabi
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The only thing this conditional is doing is adding an additional dependency on libc++ if we're building in tree... is there a way to add a dependency to a custom target after add_custom_target has been called?

http://reviews.llvm.org/D4414