It seems that the static library archive 'liby.a' contains build time
timestamps:
--8<---------------cut here---------------start------------->8---
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
--8<---------------cut here---------------end--------------->8---
