Adds changelog entries for merged PRs that still have the "needs-changelog" label, preparing for the upcoming release (scheduled for next week, August 3rd):
- #1777: "Make SHA256 compression runtime pluggable"
- #1860: "cmake: Emulate Libtool's behavior on NetBSD and OpenBSD"
The release note for #1860 is based on an earlier note on FreeBSD: https://github.com/bitcoin-core/secp256k1/blob/0f6baf319fcae0d7f11a44fc9b4d4899b3f8082a/CHANGELOG.md?plain=1#L39