In configure.in, starting at line 1098, the code to check if ranlib is necessary is:

# check if ranlib is necessary
AC_CACHE_CHECK(whether ranlib is necessary, libc_cv_ranlib_necessary, [dnl
cat > conftest.c <<EOF
int a;
char b;
void c(void) {}
EOF
$CC $CFLAGS $CPPFLAGS -c conftest.c
$AR cr conftest.a conftest.o
cp conftest.a conftest2.a
$RANLIB conftest.a
if cmp -s conftest.a conftest2.a; then
  libc_cv_ranlib_necessary=no
else
  libc_cv_ranlib_necessary=yes
fi

Under some infrequent timing conditions, the test can sometimes return yes when it shouldn't.  This is because ranlib adds a timestamp from byte position 24 to 33 that can differ between the creation of conftest.a and it's modification two lines later.

I suggest changing the comparison test to:

  if cmp -s -i34 conftest.a conftest2.a; then