frr: fix host build error on macOS

frr: fix host build error on macOS

Fixes:
lib/command_graph.c:16:1: error: argument to 'section' attribute is not valid for this target: mach-o section specifier requires a segment and section separated by a comma DEFINE_MTYPE_STATIC(LIB, CMD_TOKENS, "Command Tokens"); ^
./lib/memory.h:139:2: note: expanded from macro 'DEFINE_MTYPE_STATIC'
        DEFINE_MTYPE_ATTR(group, name, static, desc)                           \
        ^
./lib/memory.h:109:26: note: expanded from macro 'DEFINE_MTYPE_ATTR'
                __attribute__((section(".data.mtypes"))) = { {                 \

[1] https://github.com/FRRouting/frr/pull/6032
[2] https://github.com/FRRouting/frr/pull/15890

Signed-off-by: Georgi Valkov <gvalkov@gmail.com>