targets/audio: Fetch last Makefile.am from git

https://crrev.com/c/4322563 (>=15378.0.0) removed autotools support,
let's fetch the last known good version from git.

Fixes #4958. For now. Things will break again, likely.

targets/audio

@@ -57,6 +57,16 @@ if tail -n 1 "$log" | grep -q "^Error"; then
     fi
 fi
 
+# ChromiumOS >= 15378.0.0 removed autotools support (https://crrev.com/c/4322563),
+# fetch the last known good Makefile.am. We can still patch it as required.
+lastgoodam="c2ece09f69565afcbcf511b1693f3fe735bde511/cras/src/Makefile.am"
+mkdir -p "$CRASBUILDTMP/cras/src"
+# Do this unconditionally as extraction phase below would override the file if
+# it is still present in current ChromiumOS version.
+wget "https://chromium.googlesource.com/chromiumos/third_party/adhd/+/$lastgoodam?format=TEXT" -O- \
+    | base64 -d > "$CRASBUILDTMP/cras/src/Makefile.am"
+
+
 # Build CRAS ALSA plugin for the given architecture ($1)
 # A blank parameter means we are building for the native architecture.
 build_cras() {