Use default new C++11 ABI for std::string and std::list in libstdc++

This flag was once used as a work-around for very old linkers and has
not been needed for a long time. The ABI change does not affect the
public runtime ABI since the runtime does not expose any C++ symbols.
The ABI change does affect the size of OpenCL data structures, however
these are not exposed directly but only in the form of opaque pointers.

https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html

Author: pcolberg

CMakeLists.txt

@@ -196,7 +196,6 @@ set_target_properties(acl_objs PROPERTIES
 target_compile_features(acl_objs PRIVATE cxx_std_11)
 # These compile_definitions need to be public, since we're building an OBJECT library (?)
 target_compile_definitions(acl_objs PUBLIC
-  _GLIBCXX_USE_CXX11_ABI=0
   ACL_SUPPORT_DOUBLE=0
   ACL_HAS_STDLIB_STDIO
   CL_USE_DEPRECATED_OPENCL_1_0_APIS=1

test/CMakeLists.txt

@@ -31,7 +31,6 @@ add_executable(acl_test
 set_target_properties(acl_test PROPERTIES CXX_EXTENSIONS OFF)
 target_compile_features(acl_test PRIVATE cxx_std_11)
 target_compile_definitions(acl_test PRIVATE
-  _GLIBCXX_USE_CXX11_ABI=0
   "ACL_TARGET_BIT=${ACL_TARGET_BIT}"
   CL_USE_DEPRECATED_OPENCL_1_0_APIS=1
   CL_USE_DEPRECATED_OPENCL_1_1_APIS=1