Change #272999

Comments

lib1587: fix gcc `-Wconversion` with LibreSSL on Windows, test in CI
By exposing and reusing existing custom type via `vtls/openss.h`.

Also:
- GHA/curl-for-win: test in CI by enabling building tests.
  Cost is 45s per job, so limit it to the gcc job.

Seen with Windows x64 gcc (not tested in CI prior to this patch):
```
tests/libtest/lib1587.c:50:7: error: conversion from 'opt1587' {aka 'long long unsigned int'} to 'long int' may change value [-Werror=conversion]
   50 |       SSL_CTX_set_options(info->internals, opts);
      |       ^~~~~~~~~~~~~~~~~~~
tests/libtest/lib1587.c:59:7: error: conversion from 'opt1587' {aka 'long long unsigned int'} to 'long int' may change value [-Werror=conversion]
   59 |       SSL_set_options(info->internals, opts);
      |       ^~~~~~~~~~~~~~~
```
Ref: https://github.com/curl/curl/actions/runs/28258372229/job/83727170184?pr=22195#step:3:4884

Ref: da2f05e6f6cee66ea46b8b1ca3943e5a6dde0b91 #22198
Ref: 616356646159379ab091502cdc90113dc8cc11eb #22197
Follow-up to 3e40ccb87581b0f6180fbd9c1eef9c50f270c806 #21290
Follow-up to 2db8ae480fdcae7f005bf847fbbf837821c8184c #17809 #17801

Closes #22195

Changed files

• .github/workflows/curl-for-win.yml
• lib/vtls/openssl.c
• lib/vtls/openssl.h
• tests/libtest/lib1587.c