[Freeipa-devel] [freeipa PR#718][comment] configure: fix AC_CHECK_LIB usage

[lslebodn]

  URL: https://github.com/freeipa/freeipa/pull/718
Title: #718: configure: fix AC_CHECK_LIB usage

lslebodn commented:
"""
>It does not explicitly say what constitutes an unspecified value though.
```[]``` means default action.

BTW it is not peculiar behaviour because most project define custom LIBS using the 3rd argument
and not after invocation of macro.
e.g.
```
AC_CHECK_HEADER(krad.h, [], [AC_MSG_ERROR([krad.h not found])])
-AC_CHECK_LIB(krad, main, [], [AC_MSG_ERROR([libkrad not found])])
+AC_CHECK_LIB(krad, main, [KRAD_LIBS="-lkrad"], [AC_MSG_ERROR([libkrad not found])])
-KRAD_LIBS="-lkrad"
```

And link to online documentation https://www.gnu.org/software/autoconf/manual/autoconf.html#Libraries
"""

See the full comment at https://github.com/freeipa/freeipa/pull/718#issuecomment-294844095