strace: set enableParallelBuilding = true

This reduces the build time from 55s to 25s on my modern 16-core machine.

The main motivation for this step is that I apply a custom patch onto
strace in my NixOS configuration and the build time is longer than necessary.
The debian package definition shows [0] that strace can be reliably build using
multiple makefile jobs.

[0] https://github.com/strace/strace/commit/0c56f62207d81713f9ce7705e865b75f921e6a1b

pkgs/development/tools/misc/strace/default.nix

@@ -12,6 +12,8 @@ stdenv.mkDerivation rec {
   depsBuildBuild = [ buildPackages.stdenv.cc ];
   nativeBuildInputs = [ perl ];
 
+  enableParallelBuilding = true;
+
   # libunwind for -k.
   # On RISC-V platforms, LLVM's libunwind implementation is unsupported by strace.
   # The build will silently fall back and -k will not work on RISC-V.