adbd: make static.

adbd is copied into the recovery image without the accompanying
linker/libraries, so it must be a static executable.

Bug: http://b/74237641
Test: `file $ANDROID_PRODUCT_OUT/system/bin/adbd`
Change-Id: Ie8d0710f6002458519d3eea3d696e9016faafee8

adb/Android.bp

@@ -260,6 +260,9 @@ cc_binary {
     name: "adbd",
     defaults: ["adb_defaults"],
 
+    // adbd must be static, as it is copied into the recovery image.
+    static_executable: true,
+
     srcs: [
         "daemon/main.cpp",
         "daemon/mdns.cpp",