Make Linux sandbox build deterministic

It seems there are multiple reproducibility issues with the tools we use for building the Linux sandbox (as mentioned in legacy/trac#20352 (moved)):

-00b58fb0: 702e 676f 0000 2f74 6d70 2f67 6234 3537  p.go../tmp/gb457
-00b58fc0: 3938 3136 3238 2f67 6974 6875 622e 636f  981628/github.co
+00b58fb0: 702e 676f 0000 2f74 6d70 2f67 6231 3538  p.go../tmp/gb158
+00b58fc0: 3532 3636 3333 2f67 6974 6875 622e 636f  526633/github.co

But that's not the only one it seems: :(

-000001b0: 0300 0000 474e 5500 c50f b1fd 318e 7ecb  ....GNU.....1.~.
-000001c0: a61b 168e a2ec 32b6 0391 4dfb 0400 0000  ......2...M.....
-000001d0: 1400 0000 0300 0000 474e 5500 da00 559f  ........GNU...U.
-000001e0: d622 3c47 638e 0f4f 4ad1 3d2d 7e93 91e8  ."<Gc..OJ.=-~...
+000001b0: 0300 0000 474e 5500 0e56 fb68 814e 9f95  ....GNU..V.h.N..
+000001c0: b667 fc03 2349 a2d9 b0e8 922a 0400 0000  .g..#I.....*....
+000001d0: 1400 0000 0300 0000 474e 5500 6ece 2446  ........GNU.n.$F
+000001e0: 2790 d47f cfae 4b3b 3066 f673 b22b 146c  '.....K;0f.s.+.l