runtests: support multi-target cmake, drop workarounds from CI

Support multi-target cmake builds via `CURL_DIRSUFFIX` env. For example:
`export CURL_DIRSUFFIX=Debug/`.

Multi-target generators place their output to `src/<subdir>/`,
`lib/<subdir>/`, `tests/server/<subdir>`, `tests/libtest/<subdir>` and
`tests/unit/<subdir>/` by default. Before this patch, `runtests.pl`
couldn't run on such builds because it expected the binaries under the
their `<subdir>`-less directories. This patch allows to set such subdir
and make `runtests.pl` find the binaries. In CI we use multi-target
builds with tests for MSVC. It also helps Xcode-generator builds, though
in CI we don't have such job running tests.

There may be better solutions to configure this, but passing a custom
value to `runtests.pl` including its subprocesses is somewhat tricky.
The reason the configuration value expects the slash at the end is
because MSYS is automagically expanding the env to a (wrong) absolute
path if the slash is in the front.

Also:
- drop the `-DCMAKE_RUNTIME_OUTPUT_DIRECTORY_*=` workaround from CI.
- replace `resolve` references in tests with a new `%RESOLVE` variable.
  It didn't use a filename extension before. After this patch it uses
  `exe_ext('TOOL')`. I'm not sure if this is the correct choice vs.
  `exe_ext('SRV')`.
- fix `-c` option format in manual.
- fix some whitespace.

Note, in CI we still tweak `CMAKE_RUNTIME_OUTPUT_DIRECTORY_*` in jobs
which share steps between `./configure` and cmake. It's easier that way.

Ref: #15000
Cherry-picked from #16394

Closes #16452

tests/ftpserver.pl

@@ -68,16 +68,13 @@ use serverhelp qw(
     servername_str
     server_pidfilename
     server_logfilename
+    server_exe
     mainsockf_pidfilename
     mainsockf_logfilename
     datasockf_pidfilename
     datasockf_logfilename
     );
 
-use pathhelp qw(
-    exe_ext
-    );
-
 use globalconfig qw(
     $SERVERCMD
     $LOCKDIR
@@ -410,7 +407,7 @@ sub sysread_or_die {
 }
 
 sub startsf {
-    my @mainsockfcmd = ("./server/sockfilt".exe_ext('SRV'),
+    my @mainsockfcmd = (server_exe('sockfilt'),
         "--ipv$ipvnum",
         "--port", $port,
         "--pidfile", $mainsockf_pidfile,
@@ -2472,10 +2469,10 @@ sub PASV_ftp {
     logmsg "DATA sockfilt for passive data channel starting...\n";
 
     # We fire up a new sockfilt to do the data transfer for us.
-    my @datasockfcmd = ("./server/sockfilt".exe_ext('SRV'),
+    my @datasockfcmd = (server_exe('sockfilt'),
         "--ipv$ipvnum", "--port", 0,
         "--pidfile", $datasockf_pidfile,
-        "--logfile",  $datasockf_logfile);
+        "--logfile", $datasockf_logfile);
     if($nodataconn) {
         push(@datasockfcmd, '--bindonly');
     }
@@ -2694,7 +2691,7 @@ sub PORT_ftp {
     logmsg "DATA sockfilt for active data channel starting...\n";
 
     # We fire up a new sockfilt to do the data transfer for us.
-    my @datasockfcmd = ("./server/sockfilt".exe_ext('SRV'),
+    my @datasockfcmd = (server_exe('sockfilt'),
         "--ipv$ipvnum", "--connect", $port, "--addr", $addr,
         "--pidfile", $datasockf_pidfile,
         "--logfile", $datasockf_logfile);