update gc to version 7.6

[dimpase]

An update to gc is needed to support arm64/aarch64, see #23687,
as well as for FreeBSD support, see #22679.
It also appears to be good to be in sync with Linux boxes that ship make with guile extension (the latter depends on gc, and causes interesting errors, see #24575).

The source is here:
https://github.com/ivmai/bdwgc/releases/download/v7.6.4/gc-7.6.4.tar.gz

On some platforms this new version also needs libatomic_ops, see #23701

CC: @kiwifb @embray

Component: packages: standard

Author: Dima Pasechnik, Erik Bray

Branch/Commit: cd63b82

Reviewer: Erik Bray, Dima Pasechnik, Jeroen Demeyer

Issue created by migration from https://trac.sagemath.org/ticket/23700

[dimpase]

Dependencies: #23701

[dimpase]

Description changed:

--- 
+++ 
@@ -2,4 +2,4 @@
 
 The source is here: http://www.hboehm.info/gc/gc_source/gc-7.6.0.tar.gz
 
-On some platforms this new version also needs libatomic_ops.
+On some platforms this new version also needs libatomic_ops, see #23701

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

7d09a89	libatomic_ops added as standard pkg
7c8c3e3	Merge branch 'libatomic_ops' into gcupdate
277ddd7	libatomic_ops is a dependency

[sagetrac-git]

Changed commit from 37cbca1 to 277ddd7

[dimpase]

comment:3

Erik, could you please check whether this works on Cygwin without your patch?

(one need #23701 first, and re-running ./configure to register the new package)

[dimpase]

Author: Dima Pasechnik

[embray]

comment:4

Ah, yes. I remember this. I'll give it a go.

[embray]

comment:5

I think this branch needs to be updated on the latest version of #23701 since it's using 7.4.6 and this branch is using 7.4.4.

[sagetrac-git]

Changed commit from 277ddd7 to e53f784

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

4d5bbd0	libatomic_ops 7.4.6 added as standard pkg
e53f784	Merge branch 'u/dimpase/libatomic_ops' of trac.sagemath.org:sage into gcupdate