Revert "[libc++] Integrate the PSTL into libc++"

This reverts r366593, which caused unforeseen breakage on the build bots.
I'm reverting until the problems have been figured out and fixed.

git-svn-id: http://llvm.org/svn/llvm-project/libcxxabi/trunk@366603 91177308-0d34-0410-b5e6-96231b3b80d8

Author: ldionne

src/CMakeLists.txt

@@ -147,11 +147,6 @@ if (LLVM_ENABLE_MODULES)
   string(REPLACE "-Wl,-z,defs" "" CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS}")
 endif()
 
-find_package(ParallelSTL QUIET)
-if (NOT TARGET pstl::ParallelSTL)
-  message(STATUS "Could not find ParallelSTL, libc++abi will not attempt to use it but the build may fail if the libc++ in use needs it to be available.")
-endif()
-
 if ("${CMAKE_OSX_ARCHITECTURES}" MATCHES "^(armv6|armv7|armv7s)$")
   set(LIBCXXABI_USE_SJLJ_EXCEPTIONS ON)
 else()
@@ -165,9 +160,6 @@ if (LIBCXXABI_ENABLE_SHARED)
     llvm_setup_rpath(cxxabi_shared)
   endif()
   target_link_libraries(cxxabi_shared PRIVATE ${LIBCXXABI_SHARED_LIBRARIES} ${LIBCXXABI_LIBRARIES})
-  if (TARGET pstl::ParallelSTL)
-    target_link_libraries(cxxabi_shared PUBLIC pstl::ParallelSTL)
-  endif()
   set_target_properties(cxxabi_shared
                         PROPERTIES
                           CXX_EXTENSIONS
@@ -216,9 +208,6 @@ endif()
 if (LIBCXXABI_ENABLE_STATIC)
   add_library(cxxabi_static STATIC ${LIBCXXABI_SOURCES} ${LIBCXXABI_HEADERS})
   target_link_libraries(cxxabi_static PRIVATE ${LIBCXXABI_STATIC_LIBRARIES} ${LIBCXXABI_LIBRARIES})
-  if (TARGET pstl::ParallelSTL)
-    target_link_libraries(cxxabi_static PUBLIC pstl::ParallelSTL)
-  endif()
   set_target_properties(cxxabi_static
                         PROPERTIES
                           CXX_EXTENSIONS