[cmake] Use the external project machinery for libcxxabi so that it can

be disabled in CMake or relocated if desired.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213936 91177308-0d34-0410-b5e6-96231b3b80d8

projects/CMakeLists.txt

@@ -6,7 +6,8 @@ foreach(entry ${entries})
   if(IS_DIRECTORY ${entry} AND EXISTS ${entry}/CMakeLists.txt)
     if((NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/compiler-rt) AND
        (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/dragonegg) AND
-       (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/libcxx))
+       (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/libcxx) AND
+       (NOT ${entry} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR}/libcxxabi))
       add_subdirectory(${entry})
     endif()
   endif()
@@ -19,6 +20,7 @@ if(${LLVM_BUILD_RUNTIME})
   # fixed.
   if(NOT MSVC)
     add_llvm_external_project(libcxx)
+    add_llvm_external_project(libcxxabi)
   endif()
   if(NOT LLVM_BUILD_EXTERNAL_COMPILER_RT)
     add_llvm_external_project(compiler-rt)