[libc++] Fix the CMake build on Mac when setting MACOSX_DEPLOYMENT_TARGET=10.6

[hans]

Summary

The build file was trying to use LIBCXX_VERSION, which isn't set
anywhere, and also forgot to split the 'compile_flags' list.

[samsonov]

LGTM

[hans]

Closed by commit rL215463 (authored by @hans).

lib/CMakeLists.txt

 append_if(compile_flags LIBCXX_HAS_FPIC_FLAG -fPIC)
 append_if(link_flags LIBCXX_HAS_NODEFAULTLIBS_FLAG -nodefaultlibs)
 
 if ( APPLE )
   if ( CMAKE_OSX_DEPLOYMENT_TARGET STREQUAL "10.6" )
     list(APPEND compile_flags "-U__STRICT_ANSI__")
     list(APPEND link_flags
       "-compatibility_version 1"
-      "-current_version ${LIBCXX_VERSION}"
+      "-current_version 1"
       "-install_name /usr/lib/libc++.1.dylib"
       "-Wl,-reexport_library,/usr/lib/libc++abi.dylib"
       "-Wl,-unexported_symbols_list,${CMAKE_CURRENT_SOURCE_DIR}/libc++unexp.exp"
       "/usr/lib/libSystem.B.dylib")
   else()
     if ( ${CMAKE_OSX_SYSROOT} )
       list(FIND ${CMAKE_OSX_ARCHITECTURES} "armv7" OSX_HAS_ARMV7)
       if (OSX_HAS_ARMV7)
list(APPEND link_flags
       "-install_name /usr/lib/libc++.1.dylib"
       "-Wl,-unexported_symbols_list,${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")
   endif()
 endif()
 
+string(REPLACE ";" " " compile_flags "${compile_flags}")
 string(REPLACE ";" " " link_flags "${link_flags}")
 
 set_target_properties(cxx
   PROPERTIES
     COMPILE_FLAGS "${compile_flags}"
     LINK_FLAGS    "${link_flags}"
     OUTPUT_NAME   "c++"
     VERSION       "1.0"
     SOVERSION     "1"
   )
 
 install(TARGETS cxx
   LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX}
   ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX}
   )