Recover the complicated situation after my bad merge

I made a mistake merge.  Reverting it in c778945806 undid the state
on master, but now I realize it crippled the git merge mechanism.
As the merge contained a mix of commits from `master..staging-next`
and other commits from `staging-next..staging`, it got the
`staging-next` branch into a state that was difficult to recover.

I reconstructed the "desired" state of staging-next tree by:
 - checking out the last commit of the problematic range: 4effe769e2
 - `git rebase -i --preserve-merges a8a018ddc0` - dropping the mistaken
   merge commit and its revert from that range (while keeping
   reapplication from 4effe769e2)
 - merging the last unaffected staging-next commit (803ca85c20)
 - fortunately no other commits have been pushed to staging-next yet
 - applying a diff on staging-next to get it into that state

pkgs/development/libraries/libvpx/default.nix

@@ -56,20 +56,16 @@ assert isCygwin -> unitTestsSupport && webmIOSupport && libyuvSupport;
 
 stdenv.mkDerivation rec {
   pname = "libvpx";
-  version = "1.7.0";
+  version = "1.9.0";
 
   src = fetchFromGitHub {
     owner = "webmproject";
-    repo = "libvpx";
+    repo = pname;
     rev = "v${version}";
-    sha256 = "0vvh89hvp8qg9an9vcmwb7d9k3nixhxaz6zi65qdjnd0i56kkcz6";
+    sha256 = "16xv6ambc82g14h1y0q1vyy57wp6j9fbp0nk0wd5csnrw407rhry";
   };
 
-  patches = [
-    ./CVE-2019-9232.CVE-2019-9325.CVE-2019-9371.CVE-2019-9433.patch
-  ];
-
-  postPatch = ''patchShebangs .'';
+  postPatch = "patchShebangs .";
 
   outputs = [ "bin" "dev" "out" ];
   setOutputFlags = false;
@@ -135,6 +131,12 @@ stdenv.mkDerivation rec {
                     experimentalFpMbStatsSupport ||
                     experimentalEmulateHardwareSupport) "experimental")
   ] ++ optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+    #"--extra-cflags="
+    #"--extra-cxxflags="
+    #"--prefix="
+    #"--libc="
+    #"--libdir="
+    "--enable-external-build"
     # libvpx darwin targets include darwin version (ie. ARCH-darwinXX-gcc, XX being the darwin version)
     # See all_platforms: https://github.com/webmproject/libvpx/blob/master/configure
     # Darwin versions: 10.4=8, 10.5=9, 10.6=10, 10.7=11, 10.8=12, 10.9=13, 10.10=14
@@ -159,6 +161,10 @@ stdenv.mkDerivation rec {
   buildInputs = [ ]
     ++ optionals unitTestsSupport [ coreutils curl ];
 
+  NIX_LDFLAGS = [
+    "-lpthread" # fixes linker errors
+  ];
+
   enableParallelBuilding = true;
 
   postInstall = ''moveToOutput bin "$bin" '';