strings: Unconditionally install ELF Tool Chain's strings

llvm-strings may consume a large amount of memory while reading the
input file before producing any output.

ELF Tool Chain's strings is small and lightweight, and we always install
strings regardless of WITH_/WITHOUT_TOOLCHAIN settings (as it is useful
in many contexts). Return to always installing ELF Tool Chain's version
of strings.

This reverts commit 81fa5c4a828bec9f1ead280c59c31bd423e6eeea.
This reverts commit 7ca3db1999cd967f9d6d7b259aa7af54aae14a5f.

PR: 286605
Reported by: olivier
Reviewed by: olivier, brooks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D50084