Install jemalloc2 for arm64 image (#517)

Author: itzg

build/setup-arm64

@@ -10,7 +10,9 @@ if [ "$TARGETARCH" = "arm64" ] ; then
   curl -L https://ryanfortner.github.io/box64-debs/KEY.gpg | gpg --dearmor | tee /etc/apt/trusted.gpg.d/box64-debs-archive-keyring.gpg
 
   apt-get update
-  DEBIAN_FRONTEND=noninteractive apt-get install -y "$BOX64_PACKAGE"
+  DEBIAN_FRONTEND=noninteractive apt-get install -y \
+    "$BOX64_PACKAGE" \
+    libjemalloc2
 
   apt-get clean
   rm -rf /var/lib/apt/lists/*