[CMake] Support tests in runtimes layout

[phosek]

Summary

When libunwind and libc++abi is build in the runtimes layout,
we set <PROJECT>_STANDALONE_BUILD but at the same time the condition
CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR isn't true since
we're building in llvm/runtimes. Handle this case in the CMake build
to avoid disabling tests.

[phosek]

Ping?

[smeenai]

@phosek and I discussed this on IRC, and I'm summarizing our discussion here. We're not sure if it actually makes sense for the runtimes build to set the *_STANDALONE_BUILD variables, and he was gonna play with that.

libcxxabi/CMakeLists.txt

484

This seems pretty subtle. The condition seems to care about whether we're building libc++ alongside libc++abi; perhaps adding AND NOT HAVE_LIBCXX to the condition would be enough?

libunwind/CMakeLists.txt

366

This feels a little strange because the test would suggest that LLVM_CMAKE_PATH is important for the test subdirectory, but apparently things work fine without it. Is there any other condition that could work here?

[phosek]

We came up with a better solution in D57992.

libcxxabi/CMakeLists.txt

if (LIBCXXABI_USE_LLVM_UNWINDER OR LLVM_NATIVE_ARCH MATCHES ARM)
   endif()
 endif()
 
 # Add source code. This also contains all of the logic for deciding linker flags
 # soname, etc...
 add_subdirectory(src)
 
 if (LIBCXXABI_INCLUDE_TESTS)
-  if (LIBCXXABI_STANDALONE_BUILD AND NOT LIBCXXABI_ENABLE_SHARED)
+  if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND NOT LIBCXXABI_ENABLE_SHARED)
     # We can't reasonably test the system C++ library with a static
     # libc++abi.  We either need to be able to replace libc++abi at
     # run time (with a shared libc++abi), or we need to be able to
     # replace the C++ runtime (with a non- standalone build).
     message(WARNING "The libc++abi tests aren't valid when libc++abi "
                     "is built standalone (i.e. outside of "
                     "llvm/projects/libcxxabi ) and is built without "
                     "a shared library.  Either build a shared "
                     "library, build libc++abi at the same time as "
                     "you build libc++, or do without testing.  No "
                     "check target will be available!")
   else()
     add_subdirectory(test)
     add_subdirectory(fuzz)
   endif()
 endif()

libunwind/CMakeLists.txt

 include_directories(include)
 
 add_subdirectory(src)
 
 if (LIBUNWIND_INCLUDE_DOCS)
   add_subdirectory(docs)
 endif()
 
-if (EXISTS ${LLVM_CMAKE_PATH})
+if (NOT CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR OR EXISTS ${LLVM_CMAKE_PATH})
   add_subdirectory(test)
 endif()