Fix javaparser compilation with OpenJDK 9 -target 1.9.

javaparser contains references to @javax.annotation.Generated which
is in the module java.xml.ws.annotation, which isn't available by
default.

Therefore, this CL adds that annotation via the javac command line
for this host target.

Bug: 38177569
Test: USE_R8=true EXPERIMENTAL_USE_OPENJDK=true make checkbuild

Change-Id: Iaef75f0fd1344d739517093cfb26eaff3cf9be36