Android.mk: Fix gnu++14 related build failures

Android.mk: Fix gnu++14 related build failures

This patch filters-out '-std=gnu++14' from the cflags obtained
from AOSP/KATI dummy target output to avoid the following building errors:

FAILED: src/gallium/drivers/r600/45f68e3@@r600@sta/sfn_sfn_assembler.cpp.o
...
clang++ ... -std=c++17 ... -std=gnu++14
...
In file included from ../src/gallium/drivers/r600/sfn/sfn_assembler.cpp:27:
In file included from ../src/gallium/drivers/r600/sfn/sfn_assembler.h:32:
In file included from ../src/gallium/drivers/r600/sfn/sfn_shader.h:31:
../src/gallium/drivers/r600/sfn/sfn_instr.h:369:56: error: no template named 'is_base_of_v' in namespace 'std'; did you mean 'is_base_of'?
template <typename T, typename = std::enable_if_t<std::is_base_of_v<Instr, T>>>
                                                  ~~~~~^~~~~~~~~~~~
                                                       is_base_of
/home/utente/pie-x86_kernel/external/libcxx/include/type_traits:1412:29: note: 'is_base_of' declared here
struct _LIBCPP_TEMPLATE_VIS is_base_of
                            ^
In file included from ../src/gallium/drivers/r600/sfn/sfn_assembler.cpp:27:
In file included from ../src/gallium/drivers/r600/sfn/sfn_assembler.h:32:
In file included from ../src/gallium/drivers/r600/sfn/sfn_shader.h:31:
../src/gallium/drivers/r600/sfn/sfn_instr.h:369:51: error: template argument for non-type template parameter must be an expression
template <typename T, typename = std::enable_if_t<std::is_base_of_v<Instr, T>>>
                                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/utente/pie-x86_kernel/external/libcxx/include/type_traits:439:16: note: template parameter is declared here
template <bool _Bp, class _Tp = void> using enable_if_t = typename enable_if<_Bp, _Tp>::type;
               ^
2 errors generated.

Cc: "22.2" "22.3" mesa-stable
Reviewed-by: Roman Stratiienko <r.stratiienko@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19563>