Fix build since commit 093cc00cdd
("cc-wrapper: Always export environment variables for binutils").
The apcupsd build system uses "$(STRIP)" as flags for the "install"
program. Now that $STRIP is the path to the strip binary, we cannot pass
that to "install". Fixes this:
...
COPY multimon.cgi => /nix/store/...-apcupsd-3.14.14/libexec/cgi-bin
/nix/store/...-coreutils-8.27/bin/install: cannot stat 'strip': No such file or directory
ed0f2641cb