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/runtests.pl

@@ -84,6 +84,9 @@ use Digest::MD5 qw(md5);
 use List::Util 'sum';
 use I18N::Langinfo qw(langinfo CODESET);
 
+use serverhelp qw(
+    server_exe
+    );
 use pathhelp qw(
     exe_ext
     sys_native_current_path
@@ -510,7 +513,7 @@ sub checksystemfeatures {
     @version = <$versout>;
     close($versout);
 
-    open(my $disabledh, "-|", "server/disabled".exe_ext('TOOL'));
+    open(my $disabledh, "-|", server_exe('disabled', 'TOOL'));
     @disabled = <$disabledh>;
     close($disabledh);
 
@@ -766,7 +769,7 @@ sub checksystemfeatures {
         # client has IPv6 support
 
         # check if the HTTP server has it!
-        my $cmd = "server/sws".exe_ext('SRV')." --version";
+        my $cmd = server_exe('sws')." --version";
         my @sws = `$cmd`;
         if($sws[0] =~ /IPv6/) {
             # HTTP server has IPv6 support!
@@ -774,7 +777,7 @@ sub checksystemfeatures {
         }
 
         # check if the FTP server has it!
-        $cmd = "server/sockfilt".exe_ext('SRV')." --version";
+        $cmd = server_exe('sockfilt')." --version";
         @sws = `$cmd`;
         if($sws[0] =~ /IPv6/) {
             # FTP server has IPv6 support!
@@ -784,7 +787,7 @@ sub checksystemfeatures {
 
     if($feature{"UnixSockets"}) {
         # client has Unix sockets support, check whether the HTTP server has it
-        my $cmd = "server/sws".exe_ext('SRV')." --version";
+        my $cmd = server_exe('sws')." --version";
         my @sws = `$cmd`;
         $http_unix = 1 if($sws[0] =~ /unix/);
     }