Linking against libbitman.a fails

[cfib]

Linking against libbitman.a fails, as some symbols should not be in the library file (e.g., main):

$ gcc my_bitman.c -L. -lbitman
libbitman.a(bitman.o): In function `_fini':
(.fini+0x0): multiple definition of `_fini'
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crti.o:(.fini+0x0): first defined here
libbitman.a(bitman.o): In function `data_start':
(.data+0x0): multiple definition of `__data_start'
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/Scrt1.o:(.data+0x0): first defined here
libbitman.a(bitman.o): In function `data_start':
(.data+0x8): multiple definition of `__dso_handle'
/usr/lib/gcc/x86_64-linux-gnu/7/crtbeginS.o:(.data.rel.local+0x0): first defined here
libbitman.a(bitman.o):(.rodata+0x0): multiple definition of `_IO_stdin_used'
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/Scrt1.o:(.rodata.cst4+0x0): first defined here
libbitman.a(bitman.o): In function `_start':
(.text+0x0): multiple definition of `_start'
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/Scrt1.o:(.text+0x0): first defined here
libbitman.a(bitman.o): In function `main':
(.text+0xb981): multiple definition of `main'
/tmp/ccnspFX5.o:my_bitman.c:(.text+0x0): first defined here
libbitman.a(bitman.o): In function `_init':
(.init+0x0): multiple definition of `_init'
/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/crti.o:(.init+0x0): first defined here
/usr/lib/gcc/x86_64-linux-gnu/7/crtendS.o:(.tm_clone_table+0x0): multiple definition of `__TMC_END__'
libbitman.a(bitman.o):(.data+0x10): first defined here
/usr/bin/ld: error in libbitman.a(bitman.o)(.eh_frame); no .eh_frame_hdr table will be created.
collect2: error: ld returned 1 exit status