Possible fix for parallel compilation on old debian.

src/tools/pwre/src/os_linux/pwre.pl

@@ -1460,7 +1460,7 @@ sub _build () # args: branch, subbranch, flavour, phase
           if ($hw eq "x86" && $real_hw eq "x86_64") {
             $ENV{"cross_compile"} = "-m32";
           }
-          if ($branch eq "lib" || $branch eq "wbl" || ($branch eq "exe" && $flavour ne "src")) {
+          if ($branch eq "wbl" || (($branch eq "lib" || $branch eq "exe") && ($flavour eq "gtk" || $flavour eq "qt")) || ($branch eq "lib" && $flavour eq "src")) {
             # All libraries and GUI-exe files can be compiled in parallel
             system("make -j @_") && exit 1;
           } else {