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

scripts/verify-release

@@ -39,14 +39,14 @@ tarball="${1:-}"
 
 if [ -z "$tarball" ]; then
   echo "Provide a curl release tarball name as argument"
-  exit
+  exit 1
 fi
 
 i="$(find . -maxdepth 1 -type d -name 'curl-*' | wc -l)"
 
 if test "$i" -gt 1; then
   echo "multiple curl-* entries found, disambiguate please"
-  exit
+  exit 1
 fi
 
 # check if this is in a git clone directory
@@ -115,7 +115,7 @@ else
     mv "$f" _tarballs/
   done
 fi
-cd "_tarballs"
+cd _tarballs
 
 # compare the new tarball against the original
 sha256sum -c checksum