Fix configuring and building libc++ w/o an ABI library.

Typically libc++ uses libc++abi or libcxxrt to provide the ABI and runtime bits
of the C++ STL. However we also support building w/o an ABI library entirely.
This patch fixes building libc++ w/o an ABI library (and incorporates the
`~type_info()` fix in D28211).

The main changes in this patch are:

1) Add `-DLIBCXX_CXX_ABI=default` instead of using the empty string to mean "default".
2) Fix CMake bits which treated "none" as "default" on OS X.
3) Teach the source files to respect `-D_LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY`.
4) Define ~type_info() when _LIBCPP_BUILDING_HAS_NO_ABI_LIBRARY is defined.

Unfortunately this patch doesn't help clean up the macro mess that we use to
configure for different ABI libraries.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@290839 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CMakeLists.txt

@@ -34,7 +34,7 @@ add_link_flags_if(LIBCXX_CXX_ABI_LIBRARY_PATH "-L${LIBCXX_CXX_ABI_LIBRARY_PATH}"
 add_library_flags_if(LIBCXX_COVERAGE_LIBRARY "${LIBCXX_COVERAGE_LIBRARY}")
 
 if (APPLE AND (LIBCXX_CXX_ABI_LIBNAME STREQUAL "libcxxabi" OR
-               LIBCXX_CXX_ABI_LIBNAME STREQUAL "none"))
+               LIBCXX_CXX_ABI_LIBNAME STREQUAL "default"))
   set(LIBCXX_OSX_REEXPORT_SYSTEM_ABI_LIBRARY ON)
 endif()
 

lib/abi/CMakeLists.txt

@@ -5,7 +5,7 @@ if (DEFINED TARGET_TRIPLE
     AND EXISTS "${CMAKE_CURRENT_LIST_DIR}/${TARGET_TRIPLE}.abilist"
     AND TARGET cxx_shared
     AND ("${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "libcxxabi" OR
-         (APPLE AND "${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "none"))
+         (APPLE AND "${LIBCXX_CXX_ABI_LIBNAME}" STREQUAL "default"))
     AND NOT LIBCXX_ABI_UNSTABLE
     AND LIBCXX_ABI_VERSION EQUAL "1")
     set(LIBCXX_HAS_ABILIST_CONFIGURATION 1 CACHE INTERNAL "")