stdenv: Allow changing the patch command

The `patch` utility is not fully compatible with the diffs generated by
`git`, one missing feature is the renaming of files. As GitHub exports diffs
of a PR with renames, it means that those patches are not guaranteed to work
with `patch`.

doc/stdenv/stdenv.chapter.md

@@ -667,13 +667,17 @@ The patch phase applies the list of patches defined in the `patches` variable.
 
 Set to true to skip the patch phase.
 
+##### `patchCommand` {#var-stdenv-patchCommand}
+
+The patch command to use. If not set, the `patch` utility is used.
+
 ##### `patches` {#var-stdenv-patches}
 
 The list of patches. They must be in the format accepted by the `patch` command, and may optionally be compressed using `gzip` (`.gz`), `bzip2` (`.bz2`) or `xz` (`.xz`).
 
 ##### `patchFlags` {#var-stdenv-patchFlags}
 
-Flags to be passed to `patch`. If not set, the argument `-p1` is used, which causes the leading directory component to be stripped from the file names in each patch.
+Flags to be passed to `$patchCommand`. If not set, the argument `-p1` is used, which causes the leading directory component to be stripped from the file names in each patch.
 
 ##### `prePatch` {#var-stdenv-prePatch}
 

pkgs/build-support/trivial-builders/default.nix

@@ -905,17 +905,18 @@ rec {
              ) + "-patched"
     , patches   ? []
     , postPatch ? ""
+    , patchCommand ? "patch"
     , ...
     }@args: stdenvNoCC.mkDerivation {
-      inherit name src patches postPatch;
+      inherit name src patches patchCommand postPatch;
       preferLocalBuild = true;
       allowSubstitutes = false;
       phases = "unpackPhase patchPhase installPhase";
       installPhase = "cp -R ./ $out";
     }
     # Carry `meta` information from the underlying `src` if present.
     // (optionalAttrs (src?meta) { inherit (src) meta; })
-    // (removeAttrs args [ "src" "name" "patches" "postPatch" ]);
+    // (removeAttrs args [ "src" "name" "patches" "patchCommand" "postPatch" ]);
 
   /* An immutable file in the store with a length of 0 bytes. */
   emptyFile = runCommand "empty-file" {

pkgs/stdenv/generic/setup.sh

@@ -1198,7 +1198,7 @@ patchPhase() {
         fi
         # "2>&1" is a hack to make patch fail if the decompressor fails (nonexistent patch, etc.)
         # shellcheck disable=SC2086
-        $uncompress < "$i" 2>&1 | patch "${flagsArray[@]}"
+        $uncompress < "$i" 2>&1 | ${patchCommand:-patch} "${flagsArray[@]}"
     done
 
     runHook postPatch