[libcxx] Redo adding support for building and testing with an ABI library not along linker paths

Summary:
This is the second attempt at allowing for the use of libraries that the linker cannot find. The first attempt used `CMAKE_LIBRARY_PATH` and `find_library` to select which ABI library should be used. There were a number of problems with this approach:

- `find_library` didn't work with cmake targets (ie in-tree libcxxabi build)
- It wasn't always possible to determine where `find_library` actually found your library.
- `target_link_libraries` inserted the path of the ABI library into libc++'s RPATH when `find_library` was used.
- Linking libc++ and it's ABI library is a special case. It's a lot easier to keep it simple. 

After discussion with @cbergstrum a new approach was decided upon.
This patch achieve the same ends by simply using `LIBCXX_CXX_ABI_LIBRARY_PATH` to specify where to find the library (if the linker won't find it). When this variable is defined it is simply added as a library search path when linking libc++. It is a lot easier to duplicate this behavior in LIT. It also prevents libc++ from being linked with an RPATH.






Reviewers: mclow.lists, cbergstrom, chandlerc, danalbert

Reviewed By: chandlerc, danalbert

Subscribers: chandlerc, cfe-commits

Differential Revision: http://reviews.llvm.org/D5860

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@220157 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 3 insertions, 23 deletions

diff --git a/cmake/Modules/HandleLibCXXABI.cmake b/cmake/Modules/HandleLibCXXABI.cmake
index 8a9f8632d..ff830d5f2 100644
--- a/cmake/Modules/HandleLibCXXABI.cmake
+++ b/cmake/Modules/HandleLibCXXABI.cmake
@@ -8,41 +8,21 @@
 #
 # Parameters:
 #   abidefines: A list of defines needed to compile libc++ with the ABI library
-#   abilibs   : A list of libraries to link against
+#   abilib    : The ABI library to link against.
 #   abifiles  : A list of files (which may be relative paths) to copy into the
 #               libc++ build tree for the build.  These files will also be
 #               installed alongside the libc++ headers.
 #   abidirs   : A list of relative paths to create under an include directory
 #               in the libc++ build directory.
 #
-macro(setup_abi_lib abipathvar abidefines abilibs abifiles abidirs)
+macro(setup_abi_lib abipathvar abidefines abilib abifiles abidirs)
   list(APPEND LIBCXX_CXX_FEATURE_FLAGS ${abidefines})
   set(${abipathvar} "${${abipathvar}}"
     CACHE PATH
     "Paths to C++ ABI header directories separated by ';'." FORCE
     )
 
-  # To allow for libraries installed along non-default paths we use find_library
-  # to locate the ABI libraries we want. Making sure to clean the cache before
-  # each run of find_library.
-  set(LIBCXX_CXX_ABI_LIBRARIES "")
-  foreach(alib ${abilibs})
-    # cxxabi is a cmake target and not a library.
-    # Handle this special case explicitly.
-    # Otherwise use find_library to locate the correct binary.
-    if (alib STREQUAL "cxxabi")
-      list(APPEND LIBCXX_CXX_ABI_LIBRARIES cxxabi)
-    else()
-      unset(_Res CACHE)
-      find_library(_Res ${alib})
-      if (${_Res} STREQUAL "_Res-NOTFOUND")
-        message(FATAL_ERROR "Failed to find ABI library: ${alib}")
-      else()
-        message(STATUS "Adding ABI library: ${_Res}")
-        list(APPEND LIBCXX_CXX_ABI_LIBRARIES ${_Res})
-      endif()
-    endif()
-  endforeach()
+  set(LIBCXX_CXX_ABI_LIBRARY ${abilib})
 
   set(LIBCXX_ABILIB_FILES ${abifiles})