djgpp: Inherit config from BASE_unix

Build failed on djgpp due to missing config vars 'AR' and 'ARFLAGS'.
Additionally, '-lz' was not added to 'lflags' when zlib support was
enabled.  Inheriting configuration variables from BASE_unix solves both
these issues.

CLA: trivial

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19274)

Configurations/50-djgpp.conf

@@ -4,6 +4,7 @@
 
 my %targets = (
     "DJGPP" => {
+        inherit_from     => [ "BASE_unix" ],
         CC               => "gcc",
         CFLAGS           => "-fomit-frame-pointer -O2 -Wall",
         cflags           => "-I/dev/env/WATT_ROOT/inc -DTERMIOS -DL_ENDIAN",