Merge #17483: build: Set gitian arch back to amd64

fae75306bac4c82dd07a1b85ce5dfb020e052fe8 scripted-diff: Set gitian arch back to amd64 (MarcoFalke)

Pull request description:

  This was required to allow gitian builds on non-amd64 architecture, however, it seems to break the current builds (with lxc), see https://github.com/bitcoin/bitcoin/pull/17409#issuecomment-554099626

  Also, the gititan builds wouldn't be deterministic across arches anyway, see #17468

  So instead of wasting more time on this, revert the change and hope that guix allows to compile on non-amd64 architectures.

Top commit has no ACKs.

Tree-SHA512: 801e9a30ae1b0882ef45d5eb3a3cf80f3ace3b99db046069dbd95b6162119e977e3cf3134287d1ac5d09483906206acc71e1ac34d6b74dbc533d46aaf73f5cc2

contrib/gitian-descriptors/gitian-linux.yml

@@ -5,7 +5,7 @@ distro: "ubuntu"
 suites:
 - "bionic"
 architectures:
-- "linux64"
+- "amd64"
 packages:
 - "curl"
 - "g++-aarch64-linux-gnu"

contrib/gitian-descriptors/gitian-osx-signer.yml

@@ -4,7 +4,7 @@ distro: "ubuntu"
 suites:
 - "bionic"
 architectures:
-- "linux64"
+- "amd64"
 packages:
 - "faketime"
 - "xorriso"

contrib/gitian-descriptors/gitian-osx.yml

@@ -5,7 +5,7 @@ distro: "ubuntu"
 suites:
 - "bionic"
 architectures:
-- "linux64"
+- "amd64"
 packages:
 - "ca-certificates"
 - "curl"

contrib/gitian-descriptors/gitian-win-signer.yml

@@ -4,7 +4,7 @@ distro: "ubuntu"
 suites:
 - "bionic"
 architectures:
-- "linux64"
+- "amd64"
 packages:
 - "libssl-dev" # do not merge bitcoin#13782, see https://github.com/dashpay/dash/pull/3894
 - "autoconf"

contrib/gitian-descriptors/gitian-win.yml

@@ -5,7 +5,7 @@ distro: "ubuntu"
 suites:
 - "bionic"
 architectures:
-- "linux64"
+- "amd64"
 packages:
 - "curl"
 - "g++"