[libc++] Change how CMake links libc++ with OS X.

[EricWF]

Summary

As it stands now CMake will always link against /usr/lib/libc++abi.dylib on OS X; Even when -DLIBCXX_CXX_ABI_PATH is given; Even if we are using libcxxrt as the ABI library.

Furthermore, when LIBCXX_CXX_ABI_PATH is given libc++ will end up linked against two version of libc++abi. This patch, while not pretty, changes it so that CMake will guess the location of libc++abi.dylib and attempt to link libc++ against only the version of libc++abi.dylib it has guessed.

Note: We cannot actually ensure that the libc++abi.dylib that we guessed actually exists at configure time (because it may be created between configuring and building).

Any suggestions on cleaning this up is greatly appreciated.

[EricWF]

Remove the '-rpath' switch when LIBCXX_CXX_ABI_LIBRARY_PATH is defined.

[EricWF]

Abandoning

lib/CMakeLists.txt

   add_dependencies(cxx LIBCXX_CXX_ABI_DEPS)
 endif()
 
+# We need to use a bunch of special link flags for apple in these cases.
+if (APPLE AND (LIBCXX_CXX_ABI_LIBNAME STREQUAL "none" OR
+               LIBCXX_CXX_ABI_LIBNAME STREQUAL "libcxxabi"))
+  set(APPLE_SPECIAL_LINK_CONFIG TRUE)
+endif()
+
+
+if (NOT APPLE_SPECIAL_LINK_CONFIG)
+  #if LIBCXX_CXX_ABI_LIBRARY_PATH is defined we want to add it to the search path.
+  if (DEFINED LIBCXX_CXX_ABI_LIBRARY_PATH)
+    target_link_libraries(cxx "-L${LIBCXX_CXX_ABI_LIBRARY_PATH}")
+  endif()
+  # Link libc++ to the ABI library.
+  target_link_libraries(cxx ${LIBCXX_CXX_ABI_LIBRARY})
+endif()
+
 # Generate library list.
-set(libraries ${LIBCXX_CXX_ABI_LIBRARY})
+set(libraries "")
 append_if(libraries LIBCXX_HAS_PTHREAD_LIB pthread)
 append_if(libraries LIBCXX_HAS_C_LIB c)
 append_if(libraries LIBCXX_HAS_M_LIB m)
 append_if(libraries LIBCXX_HAS_RT_LIB rt)
 append_if(libraries LIBCXX_HAS_GCC_S_LIB gcc_s)
-
-#if LIBCXX_CXX_ABI_LIBRARY_PATH is defined we want to add it to the search path.
-if (DEFINED LIBCXX_CXX_ABI_LIBRARY_PATH)
-  target_link_libraries(cxx "-L${LIBCXX_CXX_ABI_LIBRARY_PATH}")
-endif()
 target_link_libraries(cxx ${libraries})
 
 # Setup flags.
 append_if(LIBCXX_COMPILE_FLAGS LIBCXX_HAS_FPIC_FLAG -fPIC)
 append_if(LIBCXX_LINK_FLAGS LIBCXX_HAS_NODEFAULTLIBS_FLAG -nodefaultlibs)
 
-if ( APPLE )
+
+if ( APPLE_SPECIAL_LINK_CONFIG )
+  # Attempt to guess the location of libc++abi.dylib. Start by setting it to the
+  # Default location.
+  set(LIBCXX_CXX_ABI_LIBRARY_LOCATION "${CMAKE_OSX_SYSROOT}/usr/lib/libc++abi.dylib")
+  # If libc++abi is an intree CMake target get its name from the target
+  # properties.
+  if(LIBCXX_CXX_ABI_LIBRARY STREQUAL "cxxabi")
+    get_target_property(LIBCXX_CXX_ABI_LIBRARY_LOCATION TARGET cxxabi PROPERTY LOCATION)
+  # Otherwise if the user has told us where to look then construct the name
+  # from the patch.
+  elseif (LIBCXX_CXX_ABI_LIBRARY STREQUAL "c++abi" AND DEFINED LIBCXX_CXX_ABI_LIBRARY_PATH)
+    set(LIBCXX_CXX_ABI_LIBRARY_LOCATION "${LIBCXX_CXX_ABI_LIBRARY_PATH}/libc++abi.dylib")
+  endif()
   if ( CMAKE_OSX_DEPLOYMENT_TARGET STREQUAL "10.6" )
     list(APPEND LIBCXX_COMPILE_FLAGS "-U__STRICT_ANSI__")
     list(APPEND LIBCXX_LINK_FLAGS
       "-compatibility_version 1"
       "-current_version 1"
       "-install_name /usr/lib/libc++.1.dylib"
-      "-Wl,-reexport_library,/usr/lib/libc++abi.dylib"
+      "-Wl,-reexport_library,${LIBCXX_CXX_ABI_LIBRARY_LOCATION}"
       "-Wl,-unexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++unexp.exp"
+      "${LIBCXX_CXX_ABI_LIBRARY_LOCATION}"
       "/usr/lib/libSystem.B.dylib")
   else()
     if ( ${CMAKE_OSX_SYSROOT} )
       list(FIND ${CMAKE_OSX_ARCHITECTURES} "armv7" OSX_HAS_ARMV7)
       if (OSX_HAS_ARMV7)
         set(OSX_RE_EXPORT_LINE
-          "${CMAKE_OSX_SYSROOT}/usr/lib/libc++abi.dylib"
           "-Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++sjlj-abi.exp")
       else()
         set(OSX_RE_EXPORT_LINE
-          "-Wl,-reexport_library,${CMAKE_OSX_SYSROOT}/usr/lib/libc++abi.dylib")
+          "-Wl,-reexport_library,${LIBCXX_CXX_ABI_LIBRARY_LOCATION}")
       endif()
     else()
-      set (OSX_RE_EXPORT_LINE "/usr/lib/libc++abi.dylib -Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++abi${LIBCXX_LIBCPPABI_VERSION}.exp")
+      set (OSX_RE_EXPORT_LINE "-Wl,-reexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++abi${LIBCXX_LIBCPPABI_VERSION}.exp")
     endif()
 
     list(APPEND LIBCXX_LINK_FLAGS

       "-Wl,-unexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++unexp.exp"
       "${OSX_RE_EXPORT_LINE}"
       "-Wl,-force_symbols_not_weak_list,${CMAKE_CURRENT_SOURCE_DIR}/notweak.exp"
-      "-Wl,-force_symbols_weak_list,${CMAKE_CURRENT_SOURCE_DIR}/weak.exp")
+      "-Wl,-force_symbols_weak_list,${CMAKE_CURRENT_SOURCE_DIR}/weak.exp"
+      "${LIBCXX_CXX_ABI_LIBRARY_LOCATION}")
   endif()
 endif()