Reland "[CMake][libcxx] Do not rely on the existence of c++abi or unwind targets"

This relands commit r291727.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@292085 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -125,8 +125,7 @@ if (LIBCXX_CXX_ABI STREQUAL "default")
           ${LLVM_MAIN_SRC_DIR}/runtimes/libcxxabi/include
     NO_DEFAULT_PATH
   )
-  if (NOT DEFINED LIBCXX_STANDALONE_BUILD AND
-      IS_DIRECTORY "${LIBCXX_LIBCXXABI_INCLUDES_INTERNAL}")
+  if (IS_DIRECTORY "${LIBCXX_LIBCXXABI_INCLUDES_INTERNAL}")
     set(LIBCXX_CXX_ABI_LIBNAME "libcxxabi")
     set(LIBCXX_CXX_ABI_INCLUDE_PATHS "${LIBCXX_LIBCXXABI_INCLUDES_INTERNAL}")
     set(LIBCXX_CXX_ABI_INTREE 1)

lib/CMakeLists.txt

@@ -247,7 +247,8 @@ if (LIBCXX_ENABLE_STATIC)
     if (LIBCXX_CXX_ABI_LIBRARY_PATH)
       set(MERGE_ARCHIVES_SEARCH_PATHS "-L${LIBCXX_CXX_ABI_LIBRARY_PATH}")
     endif()
-    if (TARGET ${LIBCXX_CXX_ABI_LIBRARY})
+    if ((TARGET ${LIBCXX_CXX_ABI_LIBRARY}) OR
+        (${LIBCXX_CXX_ABI_LIBRARY} STREQUAL "cxxabi(_static|_shared)?" AND HAVE_LIBCXXABI))
       set(MERGE_ARCHIVES_ABI_TARGET "$<TARGET_LINKER_FILE:${LIBCXX_CXX_ABI_LIBRARY}>")
     else()
       set(MERGE_ARCHIVES_ABI_TARGET
@@ -318,7 +319,9 @@ if (LIBCXX_ENABLE_SHARED AND LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
   set(LIBCXX_INTERFACE_LIBRARY_NAMES)
   foreach(lib ${LIBCXX_INTERFACE_LIBRARIES})
     # FIXME: Handle cxxabi_static and unwind_static.
-    if (TARGET ${lib})
+    if (TARGET ${lib} OR
+        (${lib} MATCHES "cxxabi(_static|_shared)?" AND HAVE_LIBCXXABI) OR
+        (${lib} MATCHES "unwind(_static|_shared)?" AND HAVE_LIBUNWIND))
       list(APPEND LIBCXX_INTERFACE_LIBRARY_NAMES "$<TARGET_PROPERTY:${lib},OUTPUT_NAME>")
     else()
       list(APPEND LIBCXX_INTERFACE_LIBRARY_NAMES "${lib}")