aaudio: align AAudioServiceMessage for 32/64 bits

Chromebook sometimes runs 32 and 64-bit code together.
That caused messages between the code to be rejected because the
struct sizes did not match.
So we used alignas(8) to force members to 8 byte boundaries.

Bug: 155901581
Test: Launch OboeTester
Test: Tap TEST OUTPUT
Test: Tap OPEN and START
Test: You should get "MMAP YES" if MMAP is supported by the device.
Change-Id: I0cd6a59a974888ef17b06b38fa78f032d602cd57

media/libaaudio/src/binding/AAudioServiceMessage.h

@@ -44,6 +44,8 @@ typedef enum aaudio_service_event_e : uint32_t {
 struct AAudioMessageEvent {
     aaudio_service_event_t event;
     union {
+        // Align so that 32 and 64-bit code can exchange messages through shared memory.
+        alignas(8)
         double  dataDouble;
         int64_t dataLong;
     };
@@ -57,8 +59,10 @@ typedef struct AAudioServiceMessage_s {
         EVENT,
     };
 
-    code what;
+    code      what;
     union {
+        // Align so that 32 and 64-bit code can exchange messages through shared memory.
+        alignas(8)
         AAudioMessageTimestamp timestamp; // what == TIMESTAMP
         AAudioMessageEvent event;         // what == EVENT
     };