As of GCC14 implicit-int has been upgraded to an error. While this is
generally a good idea it trips up some older code (particularly in
autoconf generated configure scripts). Add -Wno-implicit-int to CFLAGS
for glibc when using an old GLIBC with a new GCC.
Fixes#2208
Signed-off-by: Chris Packham <judge.packham@gmail.com>