AC_FLAGS_WARN_ALL changes proposed for inclusion in next autoconf release

[Visser, Dale]

Autoconf developers:

I originally posted the attached proposed changes back in January, and there 
was some discussion of them then*. I did not push very hard about getting the 
changes accepted then, because I was waiting on my employer's legal department 
to sign off on the FSF copyright assignment form. Now they have done so.

The attached version is a diff rebased against the latest in the master branch 
as of today. I have tested that the functionality still works. Quoting from my 
previous submission:

"The inspiration for this comes from an earlier discussion on the 'autoconf' 
list: http://lists.gnu.org/archive/html/autoconf/2013-10/msg00025.html

The basic idea is to overall enhance the security of code built using autoconf, 
by turning on compiler warnings that the developers wouldn't otherwise think to.

The patch ports over AX_FLAGS_WARN_ALL from the autoconf archive, and invokes 
it by default within AC_PROG_CC, AC_PROG_CXX and AC_PROG_FC. Of course, a 
mechanism is provided for turning off the new behavior, i.e., restoring the 
classic "no extra warnings" mode."

Best regards,
Dale Visser

[*] See 
https://lists.gnu.org/archive/html/autoconf-patches/2014-01/msg00004.html

autoconf.patch
Description: autoconf.patch