- do not pre-fill `HAVE_LINUX_TCP_H` on Linux.
`linux/tcp.h` is a Linux kernel userspace header. It's likely
installed when using glibc and likely missing by default when using
something else, e.g. MUSL (e.g. on Alpine).
Therefore always detect it for Linux targets, and only pre-fill it for
non-Linux ones.
- do not pre-fill `HAVE_GLIBC_STRERROR_R` on Linux.
To fix it for non-glibc envs, e.g. MUSL (e.g. on Alpine).
Note, the pre-fill option is a disabled by default, internal option and
strongly not recommended outside of curl development.
Closes#19116
f30f1307c1