build: glibc on Linux defines explicit_bzero in <string.h>.

[jhb]

Summary

Don't install strings.h on such systems. The local prototype doesn't
match the native Linux one when built as C++ breaking the build of
config(8) as a bootstrap tool on some Linux systems. If the missing
prototype becomes a problem in the future,
tools/build/cross-build/include/linux/strings.h can be patched to add

Obtained from: CheriBSD
Sponsored by: DARPA

[emaste]

commit message looks like it's missing something, but otherwise OK

that said we might want to migrate our code to memset_s or meset_explicit?

[jhb]

Oh, yeah, a missing "it." at the end of the sentence.

[imp]

agree with ed, but this is good for now.