Get lots of these otherwise:
/home/pbarker/gcc/gcc-arm-none-eabi-10.3-2021.07/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: lib/libAP_Periph_libs.a(GCS_MAVLink.cpp.0.o): in function `mavlink_parse_char':
GCS_MAVLink.cpp:(.text.mavlink_parse_char+0x0): multiple definition of `mavlink_parse_char'; Tools/AP_Periph/adsb.cpp.41.o:adsb.cpp:(.text.mavlink_parse_char+0x0): first defined here
/home/pbarker/gcc/gcc-arm-none-eabi-10.3-2021.07/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld: lib/libAP_Periph_libs.a(GCS_MAVLink.cpp.0.o): in function `put_bitfield_n_by_index':
GCS_MAVLink.cpp:(.text.put_bitfield_n_by_index+0x0): multiple definition of `put_bitfield_n_by_index'; Tools/AP_Periph/adsb.cpp.41.o:adsb.cpp:(.text.put_bitfield_n_by_index+0x0): first defined here