configure.ac: Do not use AC_PROG_CC_STDC anymore
 
Commit Message
  
  
On Ubuntu 22.04 LTS, this resolves:
> configure.ac:100: warning: The macro `AC_PROG_CC_STDC' is obsolete.
Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
---
  configure.ac | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)
  
 
  
@@ -18,7 +18,7 @@ 
  #                                                                             #
  ###############################################################################
  
-AC_PREREQ([2.64])
+AC_PREREQ([2.71])
  
  AC_INIT([pakfire],
  	[0.9.27],
@@ -97,7 +97,7 @@  PKG_PROG_PKG_CONFIG
  m4_pattern_forbid([^_?PKG_[A-Z_]+$],[*** pkg.m4 missing, please install pkg-config])
  
  # C Compiler
-AC_PROG_CC_STDC
+AC_PROG_CC
  
  CC_CHECK_FLAGS_APPEND([with_cflags], [CFLAGS], [\
  	-Wall \