Add xmake to prereqs.

Bypass-Presubmit-Reason: no presubmits

Change-Id: Ic4164ece12d75c1a3351f2343ea4682e9d01cdff

install-prereqs.sh

diff --git a/install-prereqs.sh b/install-prereqs.sh
index 2584195..35c7ef3 100755
--- a/install-prereqs.sh
+++ b/install-prereqs.sh
@@ -96,6 +96,7 @@
     policykit-1
     screen
     wget
+    xmake
     xxd
     zlib1g
     zlib1g-dev