setup.sh: use -exec rather than -execdir

Busybox's `find` does not support `-execdir`, so let's uses `-exec`
instead, in the spirit of requiring the minimum features needed for
the task.

pkgs/stdenv/generic/setup.sh

@@ -1031,10 +1031,10 @@ configurePhase() {
           -executable \
           -type f \
           -name configure \
-          -execdir grep -l 'GNU Libtool is free software; you can redistribute it and/or modify' {} \; \
-          -execdir touch -r {} "$CONFIGURE_MTIME_REFERENCE" \; \
-          -execdir sed -i s_/usr/bin/file_file_g {} \;    \
-          -execdir touch -r "$CONFIGURE_MTIME_REFERENCE" {} \;
+          -exec grep -l 'GNU Libtool is free software; you can redistribute it and/or modify' {} \; \
+          -exec touch -r {} "$CONFIGURE_MTIME_REFERENCE" \; \
+          -exec sed -i s_/usr/bin/file_file_g {} \;    \
+          -exec touch -r "$CONFIGURE_MTIME_REFERENCE" {} \;
         rm -f "$CONFIGURE_MTIME_REFERENCE"
     fi