tidy-up: delete parallel/unused feature flags

Detecting headers and lib separately makes sense when headers come in
variations or with extra ones, but this wasn't the case here. These were
duplicate/parallel macros that we had to keep in sync with each other
for a working build. This patch leaves a single macro for each of these
dependencies:

- Rely on `HAVE_LIBZ`, delete parallel `HAVE_ZLIB_H`.

  Also delete CMake logic making sure these two were in sync, along with
  a toggle to turn off that logic, called `CURL_SPECIAL_LIBZ`.

  Also delete stray `HAVE_ZLIB` defines.

  There is also a `USE_ZLIB` variant in `lib/config-dos.h`. This patch
  retains it for compatibility and deprecates it.

- Rely on `USE_LIBSSH2`, delete parallel `HAVE_LIBSSH2_H`.

  Also delete `LIBSSH2_WIN32`, `LIBSSH2_LIBRARY` from
  `winbuild/MakefileBuild.vc`, these have a role when building libssh2
  itself. And `CURL_USE_LIBSSH`, which had no use at all.

  Also delete stray `HAVE_LIBSSH2` defines.

- Rely on `USE_LIBSSH`, delete parallel `HAVE_LIBSSH_LIBSSH_H`.

  Also delete `LIBSSH_WIN32`, `LIBSSH_LIBRARY` and `HAVE_LIBSSH` from
  `winbuild/MakefileBuild.vc`, these were the result of copy-pasting the
  libssh2 line, and were not having any use.

- Delete unused `HAVE_LIBPSL_H` and `HAVE_LIBPSL`.

Reviewed-by: Daniel Stenberg

Closes #9652

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/vssh/ssh.h b/lib/vssh/ssh.h
index 7e1d8159c..13bb8aa2d 100644
--- a/lib/vssh/ssh.h
+++ b/lib/vssh/ssh.h
@@ -26,10 +26,10 @@
 
 #include "curl_setup.h"
 
-#if defined(HAVE_LIBSSH2_H)
+#if defined(USE_LIBSSH2)
 #include <libssh2.h>
 #include <libssh2_sftp.h>
-#elif defined(HAVE_LIBSSH_LIBSSH_H)
+#elif defined(USE_LIBSSH)
 #include <libssh/libssh.h>
 #include <libssh/sftp.h>
 #elif defined(USE_WOLFSSH)