allow old code to get compiled

debian/rules

@@ -1,6 +1,12 @@
 #!/usr/bin/make -f
 
 export DH_VERBOSE=1
+# Make sure the decades-old source code gets compiled by allowing implicit
+# function declarations and, for gcc-14 and above, by downgrading the
+# diagnostics applied by the compiler. See
+# https://gcc.gnu.org/onlinedocs/gcc-14.1.0/gcc/Warning-Options.html
+# for further details.
+export DEB_CFLAGS_MAINT_STRIP=-Werror=implicit-function-declaration
 
 %:
 	dh $@