bmake.passthru.setupHook: set some defaults

These are all read from the environment by the default bmake
stdlib (e.g. <bsd.prog.mk>, <bsd.own.mk>). Some of the default
values (like building cat pages instead of man pages, or stripping
binaries when installing) don't really make sense for Nixpkgs, so we
override them here for every build using bmake.

Eventually I'd like to unify the bmake setupHook and the NetBSD make
setupHook, but not today.

pkgs/development/tools/build-managers/bmake/setup-hook.sh

···
+addMakeFlags() {
+    export prefix="$out"
+    export MANDIR="${!outputMan}/share/man"
+    export MANTARGET=man
+    export BINOWN=
+    export STRIP_FLAG=
+}
+
+preConfigureHooks+=(addMakeFlags)
+
 bmakeBuildPhase() {
     runHook preBuild
 

pkgs/servers/http/bozohttpd/default.nix

···
     ++ optional (stdenv.hostPlatform.libc != "libSystem") "-lcrypt"
     ++ optional (luaSupport) "-llua"
     ++ optionals (sslSupport) [ "-lssl" "-lcrypto" ];
-  makeFlags = [ "LDADD=$(_LDADD)" "prefix=$(out)" "MANDIR=$(out)/share/man" "BINOWN=" ];
+  makeFlags = [ "LDADD=$(_LDADD)" ];
 
   doCheck = true;
   checkInputs = [ inetutils wget ];