treewide: use runtimeShell instead of stdenv.shell whenever possible

Whenever we create scripts that are installed to $out, we must use runtimeShell
in order to get the shell that can be executed on the machine we create the
package for. This is relevant for cross-compiling. The only use case for
stdenv.shell are scripts that are executed as part of the build system.
Usages in checkPhase are borderline however to decrease the likelyhood
of people copying the wrong examples, I decided to use runtimeShell as well.

pkgs/tools/misc/fzf/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, ncurses, buildGoPackage, fetchFromGitHub, writeText }:
+{ stdenv, ncurses, buildGoPackage, fetchFromGitHub, writeText, runtimeShell }:
 
 buildGoPackage rec {
   name = "fzf-${version}";
@@ -47,7 +47,7 @@ buildGoPackage rec {
 
     cp -R $src/shell $bin/share/fzf
     cat <<SCRIPT > $bin/bin/fzf-share
-    #!${stdenv.shell}
+    #!${runtimeShell}
     # Run this script to find the fzf shared folder where all the shell
     # integration scripts are living.
     echo $bin/share/fzf

pkgs/tools/misc/odroid-xu3-bootloader/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, lib, fetchFromGitHub, coreutils, ubootOdroidXU3 }:
+{ stdenv, lib, fetchFromGitHub, coreutils, ubootOdroidXU3, runtimeShell }:
 
 stdenv.mkDerivation {
   name = "odroid-xu3-bootloader-2015-12-04";
@@ -17,7 +17,7 @@ stdenv.mkDerivation {
 
     install -Dm755 $src/sd_fuse/hardkernel_1mb_uboot/sd_fusing.1M.sh $out/bin/sd_fuse-xu3
     sed -i \
-      -e '1i#!${stdenv.shell}' \
+      -e '1i#!${runtimeShell}' \
       -e '1iPATH=${lib.makeBinPath [ coreutils ]}:$PATH' \
       -e '/set -x/d' \
       -e 's,.\/sd_fusing\.sh,sd_fuse-xu3,g' \

pkgs/tools/misc/smc/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, jre }:
+{ stdenv, fetchurl, jre, runtimeShell }:
 
 stdenv.mkDerivation rec {
   name = "smc-6.6.3";
@@ -22,7 +22,7 @@ stdenv.mkDerivation rec {
     cp misc/smc.ico "$out/share/icons/"
 
     cat > "$out/bin/smc" << EOF
-    #!${stdenv.shell}
+    #!${runtimeShell}
     ${jre}/bin/java -jar "$out/share/java/Smc.jar" "\$@"
     EOF
     chmod a+x "$out/bin/smc"

pkgs/tools/misc/umlet/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, jre, unzip }:
+{ stdenv, fetchurl, jre, unzip, runtimeShell }:
 
 stdenv.mkDerivation rec {
   major = "14";
@@ -20,7 +20,7 @@ stdenv.mkDerivation rec {
     cp -R * "$out/lib"
 
     cat > "$out/bin/umlet" << EOF
-    #!${stdenv.shell}
+    #!${runtimeShell}
 
     programDir="$out/lib"
     cd "\$programDir"

pkgs/tools/misc/xdummy/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, writeText, writeScriptBin, xorg, xkeyboard_config }:
+{ stdenv, writeText, writeScriptBin, xorg, xkeyboard_config, runtimeShell }:
 
 let
   xorgConfig = writeText "dummy-xorg.conf" ''
@@ -73,7 +73,7 @@ let
   '';
 
 in writeScriptBin "xdummy" ''
-  #!${stdenv.shell}
+  #!${runtimeShell}
   exec ${xorg.xorgserver.out}/bin/Xorg \
     -noreset \
     -logfile /dev/null \

pkgs/tools/misc/xfstests/default.nix

@@ -1,7 +1,7 @@
 { stdenv, acl, attr, autoconf, automake, bash, bc, coreutils, e2fsprogs
 , fetchgit, fio, gawk, keyutils, killall, lib, libaio, libcap, libtool
 , libuuid, libxfs, lvm2, openssl, perl, procps, quota
-, time, utillinux, which, writeScript, xfsprogs }:
+, time, utillinux, which, writeScript, xfsprogs, runtimeShell }:
 
 stdenv.mkDerivation {
   name = "xfstests-2018-04-11";
@@ -78,7 +78,7 @@ stdenv.mkDerivation {
   # wants to write temporary files there. So create a temporary
   # to run from and symlink the runtime files to it.
   wrapperScript = writeScript "xfstests-check" ''
-    #!${stdenv.shell}
+    #!${runtimeShell}
     set -e
     export RESULT_BASE="$(pwd)/results"
 

pkgs/tools/misc/zsh-autoenv/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchFromGitHub }:
+{ stdenv, fetchFromGitHub, runtimeShell }:
 
 stdenv.mkDerivation rec {
   name = "zsh-autoenv-${version}";
@@ -18,7 +18,7 @@ stdenv.mkDerivation rec {
     cp -R $src $out/share/zsh-autoenv
 
     cat <<SCRIPT > $out/bin/zsh-autoenv-share
-    #!${stdenv.shell}
+    #!${runtimeShell}
     # Run this script to find the fzf shared folder where all the shell
     # integration scripts are living.
     echo $out/share/zsh-autoenv