stdenv: support multi-char separators in concatStringsSep

One prominent use-case for this is pytestCheckHook. This will help
making it work with structuredAttrs in the future.

pkgs/development/interpreters/python/hooks/pytest-check-hook.sh

@@ -4,29 +4,6 @@ echo "Sourcing pytest-check-hook"
 declare -ar disabledTests
 declare -a disabledTestPaths
 
-function _concatSep {
-    local result
-    local sep="$1"
-    local -n arr=$2
-    for index in ${!arr[*]}; do
-        if [ $index -eq 0 ]; then
-            result="${arr[index]}"
-        else
-            result+=" $sep ${arr[index]}"
-        fi
-    done
-    echo "$result"
-}
-
-function _pytestComputeDisabledTestsString() {
-    declare -a tests
-    local tests=($1)
-    local prefix="not "
-    prefixed=("${tests[@]/#/$prefix}")
-    result=$(_concatSep "and" prefixed)
-    echo "$result"
-}
-
 function pytestCheckPhase() {
     echo "Executing pytestCheckPhase"
     runHook preCheck
@@ -34,7 +11,7 @@ function pytestCheckPhase() {
     # Compose arguments
     args=" -m pytest"
     if [ -n "$disabledTests" ]; then
-        disabledTestsString=$(_pytestComputeDisabledTestsString "${disabledTests[@]}")
+        disabledTestsString="not $(concatStringsSep " and not " disabledTests)"
         args+=" -k \""$disabledTestsString"\""
     fi