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/servers.pm

@@ -77,6 +77,7 @@ use serverhelp qw(
     server_pidfilename
     server_portfilename
     server_logfilename
+    server_exe
     );
 
 use sshhelp qw(
@@ -1959,8 +1960,8 @@ sub runmqttserver {
     my $logfile = server_logfilename($LOGDIR, $proto, $ipvnum, $idnum);
 
     # start our MQTT server - on a random port!
-    my $cmd="server/mqttd".exe_ext('SRV').
-        " --port 0 ".
+    my $cmd=server_exe('mqttd').
+        " --port 0".
         " --pidfile $pidfile".
         " --portfile $portfile".
         " --config $LOGDIR/$SERVERCMD".
@@ -2017,7 +2018,7 @@ sub runsocksserver {
     # start our socks server, get commands from the FTP cmd file
     my $cmd="";
     if($is_unix) {
-        $cmd="server/socksd".exe_ext('SRV').
+        $cmd=server_exe('socksd').
             " --pidfile $pidfile".
             " --reqfile $LOGDIR/$SOCKSIN".
             " --logfile $logfile".
@@ -2025,8 +2026,8 @@ sub runsocksserver {
             " --backend $HOSTIP".
             " --config $LOGDIR/$SERVERCMD";
     } else {
-        $cmd="server/socksd".exe_ext('SRV').
-            " --port 0 ".
+        $cmd=server_exe('socksd').
+            " --port 0".
             " --pidfile $pidfile".
             " --portfile $portfile".
             " --reqfile $LOGDIR/$SOCKSIN".
@@ -3114,6 +3115,8 @@ sub subvariables {
     $$thing =~ s/${prefix}VERNUM/$CURLVERNUM/g;
     $$thing =~ s/${prefix}DATE/$DATE/g;
     $$thing =~ s/${prefix}TESTNUMBER/$testnum/g;
+    my $resolve = server_exe('resolve', 'TOOL');
+    $$thing =~ s/${prefix}RESOLVE/$resolve/g;
 
     # POSIX/MSYS/Cygwin curl needs: file://localhost/d/path/to
     # Windows native    curl needs: file://localhost/D:/path/to