AmigaOS: fix build fallouts, re-add to CI

Fix build issues:
- src: adjust `toolx_ftruncate()`.
- libtests/cli_ftp_upload: make `struct timeval` initialization portable.
- libtests/lib1960: do unconst in local `inet_pton()` macro.
- tests/server/dnsd: make it stub instead of failing the build.
- tests/server: make them link AmiSSL for `SocketBase`.

Also:
- bump AmiSSL to the latest release.
- add download hash checks and toolchain cache.
- sync restored code with local updates made since last year.

It takes 30 seconds per job, 1 minute in total.

Thanks-to: Bebbo
Thanks-to: Darren Banfi
Ref: https://github.com/curl/curl/pull/21989#issuecomment-4691380623
Follow-up to 7a14898264 #17486

Closes #21993

src/tool_setup.h

@@ -102,6 +102,8 @@ int toolx_ftruncate_win32(int fd, curl_off_t where);
 #elif defined(__DJGPP__)
 int toolx_ftruncate_djgpp(int fd, curl_off_t where);
 #define toolx_ftruncate toolx_ftruncate_djgpp
+#elif defined(__AMIGA__)
+#define toolx_ftruncate(f, o) ftruncate(f, (off_t)(o))
 #else
 #define toolx_ftruncate ftruncate
 #endif