kiss: Add environment variable to toggle stripping.

This commit adds KISS_STRIP to allow stripping to be controlled at
runtime for all staged packages. This is also handy when temporarily
needing debugging symbols for a given piece of software.

Defaults to '1', set to '0' to disable stripping.

Example:

KISS_STRIP=0 kiss b zlib

kiss

@@ -376,7 +376,7 @@ pkg_order() {
 pkg_strip() {
     # Strip package binaries and libraries. This saves space on the system as
     # well as on the tarballs we ship for installation.
-    [ -f "$mak_dir/$pkg/nostrip" ] && return
+    [ -f "$mak_dir/$pkg/nostrip" ]  || [ "$KISS_STRIP" = 0 ] && return
 
     log "$1" "Stripping binaries and libraries"