Configure has

AC_FUNC_MKTIME

which expands to a test of mktime that fails with the freebsd
implementation. Given that, bash compiles a mktime.o file that
defines just mktime and uses localtime. That goes in a .a file
that is before libc.

The freebsd libc defines mktime in localtime.o, which also defines
localtime among other functions.

When lld sees an undefined reference to mktime from libc, it uses
the bash provided one and then tries to find a definition of
localtime. It is found on libc's localtime.o, but now we have a
duplicated error.

The reason it works with bfd is that bash doesn't use mktime
directly and the undefined reference from libc is resolved to the
libc implementation. It would also fail to link if bash itself
directly used mktime.