[libcxxabi] Do not depend on unwind when building standalone

[phosek]

Summary

When libcxxabi is being built standalone, unwind dependency is not available, so do not use it even when LLVM unwinder is being requested.

[compnerd]

Why does standalone imply that the llvm unwinder is unavailable? I could have installed the unwinder previously and then use that instead of libgcc_s.

[phosek]

It does not imply that libunwind.(so|a) is unavailable, but it does imply that CMake target unwind is unavailable because we're building libcxxabi as a standalone project. LIBCXXABI_TEST_DEPS is passed to check-libcxxabi as DEPENDS argument which is translated to add_dependencies invocation which is incorrect. add_lit_testsuite generates the rule for invoking lit, it does not actually generate the build rule, so target_link_libraries in this case would be also incorrect.

[compnerd]

Ugh. I absolutely mis-read the patch.

libcxxabi/trunk/test/CMakeLists.txt

 if (LIBCXXABI_ENABLE_SHARED)
   set(LIBCXXABI_TEST_DEPS cxxabi_shared)
 else()
   set(LIBCXXABI_TEST_DEPS cxxabi_static)
 endif()
 
 if (NOT LIBCXXABI_BUILT_STANDALONE)
   list(APPEND LIBCXXABI_TEST_DEPS cxx)
-endif()
-
   if (LIBCXXABI_USE_LLVM_UNWINDER)
     list(APPEND LIBCXXABI_TEST_DEPS unwind)
   endif()
+endif()
 
 add_lit_testsuite(check-libcxxabi "Running libcxxabi tests"
   ${CMAKE_CURRENT_BINARY_DIR}
   DEPENDS ${LIBCXXABI_TEST_DEPS}
   )