stdenv: substituteInPlace: accept multiple filenames

I don't know if getopt is available everywhere, so I did not use it.

in any case, it can be changed to use getopt in the future if
needed.

doc/stdenv/stdenv.chapter.md

@@ -913,9 +913,9 @@ substitute ./foo.in ./foo.out \
     --subst-var someVar
 ```
 
-### `substituteInPlace` \<file\> \<subs\> {#fun-substituteInPlace}
+### `substituteInPlace` \<multiple files\> \<subs\> {#fun-substituteInPlace}
 
-Like `substitute`, but performs the substitutions in place on the file \<file\>.
+Like `substitute`, but performs the substitutions in place on the files passed.
 
 ### `substituteAll` \<infile\> \<outfile\> {#fun-substituteAll}
 

pkgs/stdenv/generic/setup.sh

@@ -771,9 +771,18 @@ substitute() {
 }
 
 substituteInPlace() {
-    local fileName="$1"
-    shift
-    substitute "$fileName" "$fileName" "$@"
+    local -a fileNames=()
+    for arg in "$@"; do
+        if [[ "$arg" = "--"* ]]; then
+            break
+        fi
+        fileNames+=("$arg")
+        shift
+    done
+
+    for file in "${fileNames[@]}"; do
+        substitute "$file" "$file" "$@"
+    done
 }
 
 _allFlags() {