Revert "_build.sh: enable `_FORTIFY_SOURCE=3` for Windows [ci skip]"

This reverts commit 7cd391b.

(See discussion curl#80)

Workaround for Debian 12 (see issue 75)

Implement CW_CONFIG=fnx flavor

Reference: 2680dce

Implement CW_CONFIG=fnx flavor

References:
* 48a930d
* fe52211

Merge commit '74ec231213493f583f2bb24efe72a19d7ee6f418' into fnx/v8.2.x

Merge branch 'main' into fnx/v8.2.x

Merge branch 'main' into fnx/v8.2.x

Enable ALTSVC at FNX flavor (closes #1)

Enable ALTSVC at FNX flavor (closes #1)

Implement CW_CONFIG=fnx flavor