Do not strip binaries manually unless you have to. All binaries should be stripped, but the INSTALL_PROGRAM macro will install and strip a binary at the same time (see the next section).
If you need to strip a file, but do not wish to use the INSTALL_PROGRAM macro, ${STRIP_CMD} will strip your program. This is typically done within the post-install target. For example:
post-install:
${STRIP_CMD} ${PREFIX}/bin/xdl
Use the file(1) command on the installed executable to check whether the binary is stripped or not. If it does not say not stripped, it is stripped. Additionally, strip(1) will not strip a previously stripped program; it will instead exit cleanly.