Fix one of upstream non-determinism, tracked here:

https://github.com/JuliaLang/julia/issues/34115
https://github.com/JuliaLang/julia/issues/25900


Patch by Nicoló Balzarotti <nicolo@nixo.xyz>.

--- a/base/loading.jl
+++ b/base/loading.jl
@@ -807,7 +807,10 @@
         path = normpath(joinpath(dirname(prev), _path))
     end
     if _track_dependencies[]
-        push!(_require_dependencies, (mod, path, mtime(path)))
+          push!(_require_dependencies,
+                (mod, path,
+                 haskey(ENV, "SOURCE_DATE_EPOCH") ?
+                 parse(Float64, ENV["SOURCE_DATE_EPOCH"]) : mtime(path)))
     end
     return path, prev
 end
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<div class='path'>path: <a href='/guix/log/?id=0836ef6b69a1fb4d26ad3b33bb1d4e32a6f872bd'>root</a>/<a href='/guix/log/tests?id=0836ef6b69a1fb4d26ad3b33bb1d4e32a6f872bd'>tests</a>/<a href='/guix/log/tests/guix-graph.sh?id=0836ef6b69a1fb4d26ad3b33bb1d4e32a6f872bd'>guix-graph.sh</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/guix-graph.sh?id=0836ef6b69a1fb4d26ad3b33bb1d4e32a6f872bd&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-09-28 21:06:36 -0500'>2020-09-28</span></td><td><a href='/guix/commit/tests/guix-graph.sh?id=d8934360d2453a403b5433e71d09188e4ed23b57'>tests: Simplify shell exit status negation;</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/guix-archive.sh, tests/guix-build-branch.sh, tests/guix-build.sh,
tests/guix-daemon.sh, tests/guix-download.sh, tests/guix-environment.sh,
tests/guix-gc.sh, tests/guix-git-authenticate.sh, tests/guix-graph.sh,
tests/guix-hash.sh, tests/guix-lint.sh, tests/guix-pack-relocatable.sh,
tests/guix-pack.sh, tests/guix-package-aliases.sh, tests/guix-package-net.sh,
tests/guix-package.sh: Use the shell '!' keyword to negate command exit status
in place of 'if ...; then false; else true; fi'
</span></span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2020-05-11 23:30:55 +0200'>2020-05-11</span></td><td><a href='/guix/commit/tests/guix-graph.sh?id=88a96c568c47c97d05d883ada5afbc4e1200b10f'>guix graph: Add '--path'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/graph.scm (display-path): New procedure.
(%options, show-help): Add '--path'.
(guix-graph): Handle it.
* tests/guix-graph.sh: Add tests.
* doc/guix.texi (Invoking guix graph): Document it.
(Invoking guix size): Mention it.
</span></span></td><td>Ludovic Courtès</td></tr>