Add '--prebuilts' build option.

This option will build emulator prebuilts (e.g. Qt6).

Bug: 299464843
Test: tools/buildSrc/servers/build_tools.py --prebuilts
Change-Id: Ic8a1200ba5dab100034097c32ac5431de55382d7
diff --git a/servers/build_tools.py b/servers/build_tools.py
index 9dbe28e..0c6ad00 100755
--- a/servers/build_tools.py
+++ b/servers/build_tools.py
@@ -88,6 +88,13 @@
         help="Build the emulator with the gfxstream libraries",
     )
     parser.add_argument(
+        "--prebuilts",
+        dest="prebuilts",
+        action="store",
+        nargs="*",
+        help="Builds the specified prebuilts (i.e. --prebuilts qt ffmpeg), or all prebuilts if no argument is provided",
+    )
+    parser.add_argument(
         "--enable_system_rust",
         action="store_true",
         help="Build the emulator with the System Rust on the host machine",
@@ -152,6 +159,8 @@
         cmd = cmd + ["--feature", "enable_system_rust"]
     if args.with_debug:
         cmd = cmd + ["--config", "debug"]
+    if args.prebuilts is not None:
+        cmd = cmd + ["--prebuilts"] + args.prebuilts
 
     # Make sure the dist directory exists.
     os.makedirs(args.dist_dir, exist_ok=True)