Removed AC_PROG_CC_STDC again. It enforces C99/gnu99 stdandard which is too

liberal for me. Also, autoconf 2.61 and earlier doesn't work with icc 10.1
for this macro. (2.62 confirmed to work though). See discusson on the mailing
list starting here:

http://daniel.haxx.se/projects/c-ares/mail/c-ares-archive-2008-05/0001.shtml