gpm: pull patch pending upstream inclusion to fix parallel install

Without the change when install parallelism is enabled it fails as:

    install -c gpm ../gpm-unstable-2020-06-17/sbin/gpm
    install: cannot create regular file '../gpm-unstable-2020-06-17/sbin/gpm': No such file or directory

pkgs/servers/gpm/default.nix

@@ -27,6 +27,14 @@ stdenv.mkDerivation rec {
       url = "https://github.com/kaction/gpm/commit/217b4fe4c9b62298a4e9a54c1f07e3b52b013a09.patch";
       sha256 = "1f74h12iph4z1dldbxk9imcq11805c3ai2xhbsqvx8jpjrcfp19q";
     })
+
+    # Pull fix pending upstream inclusion to fix parallel installation:
+    #   https://github.com/telmich/gpm/pull/43
+    (fetchpatch {
+      name = "parallel-install.patch";
+      url = "https://github.com/telmich/gpm/commit/a88fb82a7afe96e872bb31c554e9ad5888f5a451.patch";
+      sha256 = "0g1jhz9bjw7vqjv922xkhs8xkjxdqh11nj38jj3c8nv5lcil76nx";
+    })
   ];
   preConfigure = ''
     ./autogen.sh
@@ -38,6 +46,8 @@ stdenv.mkDerivation rec {
     (if ncurses == null then "--without-curses" else "--with-curses")
   ];
 
+  enableParallelBuilding = true;
+
   # Provide libgpm.so for compatability
   postInstall = ''
     ln -sv $out/lib/libgpm.so.2 $out/lib/libgpm.so