Obsolete autoconf macros

[tgurr]

With autoconf 2.71 there are some warnings:

configure.ac:90: warning: The macro `AC_PROG_CC_C99' is obsolete.
configure.ac:90: You should run autoupdate.
./lib/autoconf/c.m4:1659: AC_PROG_CC_C99 is expanded from...
configure.ac:90: the top level
configure.ac:94: warning: The macro `AC_PROG_LD' is obsolete.
configure.ac:94: You should run autoupdate.
m4/libtool.m4:3330: AC_PROG_LD is expanded from...
configure.ac:94: the top level
configure.ac:163: warning: The macro `AC_TRY_COMPILE' is obsolete.
configure.ac:163: You should run autoupdate.
./lib/autoconf/general.m4:2847: AC_TRY_COMPILE is expanded from...
configure.ac:163: the top level

Here's what I could find:

AC_PROG_CC_C99

*** AC_PROG_CC_STDC, AC_PROG_CC_C89, AC_PROG_CC_C99 are now obsolete.
  Applications should use AC_PROG_CC.

https://lwn.net/Articles/839395/

AC_PROG_LD

AC_PROG_LD is a old macro from libtool (though more aptly named), you
should use LT_PATH_LD instead.

https://lists.gnu.org/archive/html/autoconf/2010-05/msg00016.html

AC_TRY_COMPILE

AC_TRY_COMPILE replaced by AC_COMPILE_IFELSE

https://www.gnu.org/software/autoconf/manual/autoconf-2.70/html_node/Obsolete-Macros.html