gawk: Add runtimeShell to buildInputs

This package distributes shell scripts in /bin. Its shebangs are
always patched to a /nix/store shell, but by default, they are patched to
use the stdenv's shell, which during bootstrap is build in the previous
stdenv. By using runtimeShell from the current stdenv, we can shorten the
FreeBSD bootstrap process significantly.

pkgs/tools/text/gawk/default.nix

@@ -1,4 +1,5 @@
 { lib, stdenv, fetchurl
+, runtimeShellPackage
 # TODO: links -lsigsegv but loses the reference for some reason
 , withSigsegv ? (false && stdenv.hostPlatform.system != "x86_64-cygwin"), libsigsegv
 , interactive ? false, readline
@@ -39,7 +40,9 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [ autoreconfHook ]
     ++ lib.optional (doCheck && stdenv.isLinux) glibcLocales;
 
-  buildInputs = lib.optional withSigsegv libsigsegv
+  buildInputs = [
+    runtimeShellPackage
+  ] ++ lib.optional withSigsegv libsigsegv
     ++ lib.optional interactive readline
     ++ lib.optional stdenv.isDarwin locale;