tidy-up: syntax and code nits

- cmp-pkg-config.sh: replace `-r -f` with `-rf` to match rest of repo.
- configure.ac: add double quotes for robustness (not a bug).
- curl-openssl.m4: merge nested `if`s.
- CurlTests.c: drop `!= 0`, also to sync with m4.
- CurlTests.c: replace `example.com` with `localhost` in
  `gethostbyname()` feature test code. (compile-only, not a bug)
- GHA/http3-linux: drop literal `true` from bool expression.
- lib650: drop redundant `&`.
- move variable/call to left-hand side of equality checks, where
  missing.
- perl: detach `<`/`>` from filename in `open()`, where missing.
- schannel: apply two nit fixes lost in rebase.
- scripts/verify-release: drop redundant double quotes.
- scripts/verify-release: exit with error code on error.
- synctime: replace magic numbers with `sizeof()`.
- telnet: add missing parentheses to macro value.
- tests/Makefile.am: use single quotes.
- tool_operate: drop redundant `break` after `return` in VMS code.
- unit2413: drop unused NULL pointer + free call.
- unit2413: fix duplicate test case name.
- urlapi: drop redundant parentheses.
- urlapi: drop `CURL_UNCONST()` that became redundant.

Closes #22186

tests/server/util.c

@@ -657,31 +657,31 @@ void install_signal_handlers(bool keep_sigalrm)
 void restore_signal_handlers(bool keep_sigalrm)
 {
 #ifdef SIGHUP
-  if(SIG_ERR != old_sighup_handler)
+  if(old_sighup_handler != SIG_ERR)
     (void)set_signal(SIGHUP, old_sighup_handler, FALSE);
 #endif
 #ifdef SIGPIPE
-  if(SIG_ERR != old_sigpipe_handler)
+  if(old_sigpipe_handler != SIG_ERR)
     (void)set_signal(SIGPIPE, old_sigpipe_handler, FALSE);
 #endif
 #ifdef SIGALRM
   if(!keep_sigalrm) {
-    if(SIG_ERR != old_sigalrm_handler)
+    if(old_sigalrm_handler != SIG_ERR)
       (void)set_signal(SIGALRM, old_sigalrm_handler, FALSE);
   }
 #else
   (void)keep_sigalrm;
 #endif
 #ifdef SIGINT
-  if(SIG_ERR != old_sigint_handler)
+  if(old_sigint_handler != SIG_ERR)
     (void)set_signal(SIGINT, old_sigint_handler, FALSE);
 #endif
 #ifdef SIGTERM
-  if(SIG_ERR != old_sigterm_handler)
+  if(old_sigterm_handler != SIG_ERR)
     (void)set_signal(SIGTERM, old_sigterm_handler, FALSE);
 #endif
 #if defined(SIGBREAK) && defined(_WIN32)
-  if(SIG_ERR != old_sigbreak_handler)
+  if(old_sigbreak_handler != SIG_ERR)
     (void)set_signal(SIGBREAK, old_sigbreak_handler, FALSE);
 #endif
 #ifdef _WIN32