build: Replace use of deprecated autoconf macro AC_PROG_CC_C89

According to [autoconf 2.70](https://www.gnu.org/software/autoconf/manual/autoconf-2.70/html_node/Obsolete-Macros.html)
documentation, the `AC_PROG_CC_C89' is replaced by `AC_PROG_CC`, which
defines the same variable `ac_cv_prog_cc_c89`.

Avoids the following message:
```
configure.ac:23: warning: The macro `AC_PROG_CC_C89' is obsolete.
```

Author: laanwj

configure.ac

@@ -39,7 +39,7 @@ AC_PATH_TOOL(RANLIB, ranlib)
 AC_PATH_TOOL(STRIP, strip)
 
 AM_PROG_CC_C_O
-AC_PROG_CC_C89
+AC_PROG_CC
 if test x"$ac_cv_prog_cc_c89" = x"no"; then
   AC_MSG_ERROR([c89 compiler support required])
 fi