lib: make CURLX_SET_BINMODE() and use it

Use it from libtests' `first.c` and thus also from units, and tunits.

Also:
- cmake: drop stray `curltool` lib dependency for units.
- units: stop depending on `src` headers.
- tests/server: drop depending on `src` headers.
  (the remaining one listed in the comments, `tool_xattr.h`, was not
  actually used from servers.)
- tests/server: drop duplicate curlx headers.
  (Except `warnless.h`, which is tricky on Windows.)

Closes #17672

tests/libtest/CMakeLists.txt

@@ -54,7 +54,6 @@ target_include_directories(${BUNDLE} PRIVATE
   "${PROJECT_BINARY_DIR}/lib"            # for "curl_config.h"
   "${PROJECT_SOURCE_DIR}/lib"            # for "curl_setup.h"
   "${PROJECT_SOURCE_DIR}/lib/curlx"      # for curlx
-  "${PROJECT_SOURCE_DIR}/src"            # for "tool_binmode.h"
   "${CMAKE_CURRENT_SOURCE_DIR}"          # for the generated bundle source to find included test sources
   "${PROJECT_SOURCE_DIR}/tests/unit"     # for "curlcheck.h"
 )

tests/libtest/Makefile.am

@@ -37,7 +37,6 @@ AM_CPPFLAGS = -I$(top_srcdir)/include        \
               -I$(top_builddir)/lib          \
               -I$(top_srcdir)/lib            \
               -I$(top_srcdir)/lib/curlx      \
-              -I$(top_srcdir)/src            \
               -I$(srcdir)                    \
               -I$(top_srcdir)/tests/unit
 

tests/libtest/first.c

@@ -27,7 +27,7 @@
 
 #include "memdebug.h"
 #include "curlx/timediff.h"
-#include "tool_binmode.h"
+#include "curlx/binmode.h"
 
 int select_wrapper(int nfds, fd_set *rd, fd_set *wr, fd_set *exc,
                    struct timeval *tv)
@@ -107,7 +107,7 @@ int main(int argc, char **argv)
   char *env;
   size_t tmp;
 
-  CURL_SET_BINMODE(stdout);
+  CURLX_SET_BINMODE(stdout);
 
   memory_tracking_init();