db: disable dbm support by default

pkgs/development/libraries/db/generic.nix

@@ -1,6 +1,7 @@
 { stdenv, fetchurl
 , cxxSupport ? true
 , compat185 ? true
+, dbmSupport ? false
 
 # Options from inherited versions
 , version, sha256
@@ -19,12 +20,13 @@ stdenv.mkDerivation (rec {
 
   patches = extraPatches;
 
-  configureFlags = [
-    (if cxxSupport then "--enable-cxx" else "--disable-cxx")
-    (if compat185 then "--enable-compat185" else "--disable-compat185")
-    "--enable-dbm"
-    (stdenv.lib.optionalString stdenv.isFreeBSD "--with-pic")
-  ];
+  configureFlags =
+    [
+      (if cxxSupport then "--enable-cxx" else "--disable-cxx")
+      (if compat185 then "--enable-compat185" else "--disable-compat185")
+    ]
+    ++ stdenv.lib.optional dbmSupport "--enable-dbm"
+    ++ stdenv.lib.optional stdenv.isFreeBSD "--with-pic";
 
   preConfigure = ''
     cd build_unix