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

lib/Makefile.m32

@@ -132,7 +132,7 @@ ifneq ($(findstring -rtmp,$(CFG)),)
 endif
 ifneq ($(findstring -ssh2,$(CFG)),)
   LIBSSH2_PATH ?= $(PROOT)/../libssh2
-  CPPFLAGS += -DUSE_LIBSSH2 -DHAVE_LIBSSH2_H
+  CPPFLAGS += -DUSE_LIBSSH2
   CPPFLAGS += -I"$(LIBSSH2_PATH)/include"
   _LDFLAGS += -L"$(LIBSSH2_PATH)/lib"
   _LDFLAGS += -L"$(LIBSSH2_PATH)/win32"
@@ -187,7 +187,7 @@ endif
 ifneq ($(findstring -zlib,$(CFG))$(ZLIB),)
   ZLIB_PATH ?= $(PROOT)/../zlib
   # These CPPFLAGS are also required when compiling the curl tool via 'src'.
-  CPPFLAGS += -DHAVE_LIBZ -DHAVE_ZLIB_H
+  CPPFLAGS += -DHAVE_LIBZ
   CPPFLAGS += -I"$(ZLIB_PATH)"
   _LDFLAGS += -L"$(ZLIB_PATH)"
   _LIBS += -lz

lib/config-amigaos.h

@@ -65,7 +65,6 @@
 #define HAVE_UTIME 1
 #define HAVE_UTIME_H 1
 #define HAVE_WRITABLE_ARGV 1
-#define HAVE_ZLIB_H 1
 #define HAVE_SYS_IOCTL_H 1
 
 #define NEED_MALLOC_H 1

lib/config-dos.h

@@ -105,9 +105,7 @@
 /* CURLDEBUG definition enables memory tracking */
 /* #define CURLDEBUG */
 
-/* USE_ZLIB on cmd-line */
-#ifdef USE_ZLIB
-  #define HAVE_ZLIB_H            1
+#ifdef USE_ZLIB  /* Deprecated. Use HAVE_LIBZ instead. */
   #define HAVE_LIBZ              1
 #endif
 

lib/config-plan9.h

@@ -141,8 +141,6 @@
 #define HAVE_UTIME 1
 #define HAVE_UTIME_H 1
 
-#define HAVE_ZLIB_H 1
-
 #define HAVE_POSIX_STRERROR_R 1
 #define HAVE_STRERROR_R 1
 

lib/content_encoding.c

@@ -28,7 +28,7 @@
 #include <curl/curl.h>
 #include <stddef.h>
 
-#ifdef HAVE_ZLIB_H
+#ifdef HAVE_LIBZ
 #include <zlib.h>
 #endif
 

lib/curl_config.h.cmake

@@ -343,21 +343,9 @@
 /* Define to 1 if you have the `socket' library (-lsocket). */
 #cmakedefine HAVE_LIBSOCKET 1
 
-/* Define to 1 if you have the `psl' library (-lpsl). */
-#cmakedefine HAVE_LIBPSL 1
-
-/* Define to 1 if you have the <libpsl.h> header file. */
-#cmakedefine HAVE_LIBPSL_H 1
-
 /* Define to 1 if you have the `ssh2' library (-lssh2). */
 #cmakedefine HAVE_LIBSSH2 1
 
-/* Define to 1 if you have the <libssh2.h> header file. */
-#cmakedefine HAVE_LIBSSH2_H 1
-
-/* Define to 1 if you have the <libssh/libssh.h> header file. */
-#cmakedefine HAVE_LIBSSH_LIBSSH_H 1
-
 /* if zlib is available */
 #cmakedefine HAVE_LIBZ 1
 
@@ -604,9 +592,6 @@
 /* Define if you have the <process.h> header file. */
 #cmakedefine HAVE_PROCESS_H 1
 
-/* if you have the zlib.h header file */
-#cmakedefine HAVE_ZLIB_H 1
-
 /* Define to 1 if you need the lber.h header file even with ldap.h */
 #cmakedefine NEED_LBER_H 1
 

lib/urldata.h

@@ -185,10 +185,10 @@ typedef CURLcode (*Curl_datastream)(struct Curl_easy *data,
 # endif
 #endif
 
-#ifdef HAVE_LIBSSH2_H
+#ifdef USE_LIBSSH2
 #include <libssh2.h>
 #include <libssh2_sftp.h>
-#endif /* HAVE_LIBSSH2_H */
+#endif /* USE_LIBSSH2 */
 
 #define READBUFFER_SIZE CURL_MAX_WRITE_SIZE
 #define READBUFFER_MAX  CURL_MAX_READ_SIZE

lib/version.c

@@ -53,7 +53,7 @@
 #include <librtmp/rtmp.h>
 #endif
 
-#ifdef HAVE_ZLIB_H
+#ifdef HAVE_LIBZ
 #include <zlib.h>
 #endif
 

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)