stdenv: accept wider range of $configureScript options

Fixes #12632.

I think it's better to quote this variable in general, because it is
common and even documented to pass space-separated commands in there.
The greps should just fail in that case and `if` won't proceed
which seems fine for such cases, and it's certainly better than
passing additional unintended parameters to grep
(which was happening all the time before).

pkgs/stdenv/generic/setup.sh

@@ -644,14 +644,14 @@ configurePhase() {
 
     # Add --disable-dependency-tracking to speed up some builds.
     if [ -z "$dontAddDisableDepTrack" ]; then
-        if grep -q dependency-tracking $configureScript; then
+        if grep -q dependency-tracking "$configureScript"; then
             configureFlags="--disable-dependency-tracking $configureFlags"
         fi
     fi
 
     # By default, disable static builds.
     if [ -z "$dontDisableStatic" ]; then
-        if grep -q enable-static $configureScript; then
+        if grep -q enable-static "$configureScript"; then
             configureFlags="--disable-static $configureFlags"
         fi
     fi