liblog: Always report as debuggable when building userdebug/eng

This doesn't affect the normal behavior of our builds, because
ro.debuggable is set to 1 on userdebug/eng anyway.

However, it's helpful because making __android_log_is_debuggable
return a compile time value rather than the value of runtime prop
lets us pass checks that'd otherwise prevent us from using adb root
when Magisk is installed.

Change-Id: I36f53976162e652a38008ced459ca02fd6c0af51

liblog/Android.bp

@@ -117,6 +117,11 @@ cc_library {
         "-DLIBLOG_LOG_TAG=1006",
         "-DSNET_EVENT_LOG_TAG=1397638484",
     ],
+    product_variables: {
+        debuggable: {
+            cflags: ["-DDEBUGGABLE"],
+        },
+    },
     logtags: ["event.logtags"],
     compile_multilib: "both",
 }

liblog/properties.cpp

@@ -275,6 +275,9 @@ int __android_log_is_loggable(int prio, const char* tag, int default_prio) {
 }
 
 int __android_log_is_debuggable() {
+#ifdef DEBUGGABLE
+  return 1;
+#else
   static uint32_t serial;
   static struct cache_char tag_cache;
   static const char key[] = "ro.debuggable";
@@ -302,6 +305,7 @@ int __android_log_is_debuggable() {
   }
 
   return ret;
+#endif
 }
 
 /*