Merge bitcoin/bitcoin#22075: guix: Misc leftover usability improvements

108a6be92a guix: Check for disk space availability before building (Carl Dong)
d7dec89091 guix: Remove dest if OUTDIR mv fails (Carl Dong)

Pull request description:

  There seems to be some corner cases that can be hit when guix scripts unexpectedly fail in the middle of operation, see: https://gnusha.org/bitcoin-builds/2021-05-24.log

  - Perform an early disk space check for `guix-build`
  - Overwrite existing output directory after a successful build (the existing one might be malformed), and cleanup output directory if the `mv` somehow fails

ACKs for top commit:
  laanwj:
    Tested ACK 108a6be92a
  achow101:
    ACK 108a6be92a

Tree-SHA512: cf6438317da40bf55714cd2d8cce859b3d435cc66cabefe8d4a53552d7880966acfe84ffe8fadf1c80e368ae6b037992258a6d409df85ffc6ce8bf780e98e2e5

contrib/guix/guix-build

@@ -138,6 +138,28 @@ for host in $HOSTS; do
     esac
 done
 
+################
+# VERSION_BASE should have enough space
+################
+
+avail_KiB="$(df -Pk "$VERSION_BASE" | sed 1d | tr -s ' ' | cut -d' ' -f4)"
+total_required_KiB=0
+for host in $HOSTS; do
+    case "$host" in
+        *darwin*) required_KiB=440000 ;;
+        *mingw*)  required_KiB=7600000 ;;
+        *)        required_KiB=6400000 ;;
+    esac
+    total_required_KiB=$((total_required_KiB+required_KiB))
+done
+
+if (( total_required_KiB > avail_KiB )); then
+    total_required_GiB=$((total_required_KiB / 1048576))
+    avail_GiB=$((avail_KiB / 1048576))
+    echo "Performing a Bitcoin Core Guix build for the selected HOSTS requires ${total_required_GiB} GiB, however, only ${avail_GiB} GiB is available. Please free up some disk space before performing the build."
+    exit 1
+fi
+
 ################
 # Check that we can connect to the guix-daemon
 ################

contrib/guix/libexec/build.sh

@@ -447,4 +447,6 @@ mkdir -p "$DISTSRC"
     esac
 )  # $DISTSRC
 
-mv --no-target-directory "$OUTDIR" "$ACTUAL_OUTDIR"
+rm -rf "$ACTUAL_OUTDIR"
+mv --no-target-directory "$OUTDIR" "$ACTUAL_OUTDIR" \
+    || ( rm -rf "$ACTUAL_OUTDIR" && exit 1 )

contrib/guix/libexec/codesign.sh

@@ -100,4 +100,6 @@ mkdir -p "$DISTSRC"
     esac
 )  # $DISTSRC
 
-mv --no-target-directory "$OUTDIR" "$ACTUAL_OUTDIR"
+rm -rf "$ACTUAL_OUTDIR"
+mv --no-target-directory "$OUTDIR" "$ACTUAL_OUTDIR" \
+    || ( rm -rf "$ACTUAL_OUTDIR" && exit 1 )