Building pre 4.0-alpha results in non-deterministic Windows builds

Building 4.0-alpha bundles using a6ec17d500fadaa6ce9259ac5a7bd8150504e2a4 results in different timestamps and checksums in the PE header of libeay32.dll. The diff between https://people.torproject.org/~mikeperry/builds/4.0-alpha-1/torbrowser-install-4.0-alpha-1_de.exe and mine is:

 0000050: 6973 2070 726f 6772 616d 2063 616e 6e6f  is program canno
 0000060: 7420 6265 2072 756e 2069 6e20 444f 5320  t be run in DOS 
 0000070: 6d6f 6465 2e0d 0d0a 2400 0000 0000 0000  mode....$.......
-0000080: 5045 0000 4c01 0a00 0000 0000 0000 0000  PE..L...........
+0000080: 5045 0000 4c01 0a00 6163 6b00 0000 0000  PE..L...ack.....
 0000090: 0000 0000 e000 0e23 0b01 0218 0078 1300  .......#.....x..
 00000a0: 00e4 1900 0032 0000 2014 0000 0010 0000  .....2.. .......
 00000b0: 0090 1300 0000 0063 0010 0000 0002 0000  .......c........
 00000c0: 0400 0000 0100 0000 0400 0000 0000 0000  ................
-00000d0: 0090 1a00 0004 0000 e762 1a00 0300 0000  .........b......
+00000d0: 0090 1a00 0004 0000 b3c6 1a00 0300 0000  ................
 00000e0: 0000 2000 0010 0000 0000 1000 0010 0000  .. .............
 00000f0: 0000 0000 1000 0000 00e0 1700 20a9 0100  ............ ...
 0000100: 0090 1900 7010 0000 00d0 1900 3804 0000  ....p.......8...

This might be related to the fix for #12391 (closed).

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