bug#35569: [core-updates] bison is not reproducible

[Maxim Cournoyer]

It seems that the static library archive 'liby.a' contains build time 
timestamps:

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diffoscope --exclude-command bin/stat 
/gnu/store/aqcpvkx93zbf1zr46qi5h1yf6a1cj9i1-bison-3.3.2{,-check}
--- /gnu/store/aqcpvkx93zbf1zr46qi5h1yf6a1cj9i1-bison-3.3.2
+++ /gnu/store/aqcpvkx93zbf1zr46qi5h1yf6a1cj9i1-bison-3.3.2-check
├── lib
│ ├── liby.a
│ │ ├── file list
│ │ │ @@ -1,3 +1,3 @@
│ │ │ -----------   0        0        0       26 2019-05-04 18:09:58.000000 /
│ │ │ +----------   0        0        0       26 2019-05-04 18:09:39.000000 /
│ │ │  ?rw-r--r--   0        0        0     2648 1970-01-01 00:00:00.000000 
main.o
│ │ │  ?rw-r--r--   0        0        0     4404 1970-01-01 00:00:00.000000 
yyerror.o
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