Makefile.uk: Use -fpermissive flag

Use -fpermissive flag to allow compiler-rt build

note: (if you use ‘-fpermissive’, G++ will accept your code, but
allowing the use of an undeclared name is deprecated)

build/libcxx/origin/libcxx-15.0.0.src/include/__type_traits/is_same.h:22:72:
error: template argument 1 is invalid
   22 | struct _LIBCPP_TEMPLATE_VIS is_same :
_BoolConstant<__is_same(_Tp, _Up)> { };

Signed-off-by: Mamta Shukla <mamtashukla555@gmail.com>

Author: mamtashukla

Makefile.uk

@@ -93,7 +93,7 @@ LIBCXX_SUPPRESS_FLAGS-$(call have_gcc) += -Wno-alloc-size-larger-than
 LIBCXX_SUPPRESS_FLAGS-$(call have_gcc) += -Wno-maybe-uninitialized
 
 LIBCXX_CFLAGS-y    += $(LIBCXX_CONFIG_FLAGS)
-LIBCXX_CXXFLAGS-y  += $(LIBCXX_CONFIG_FLAGS) -std=c++2a
+LIBCXX_CXXFLAGS-y  += $(LIBCXX_CONFIG_FLAGS) -std=c++2a -fpermissive
 
 LIBCXX_CFLAGS-y   += $(LIBCXX_SUPPRESS_FLAGS-y)
 LIBCXX_CXXFLAGS-y += $(LIBCXX_SUPPRESS_FLAGS-y)