Fix alignas() on non-packed architectures (#839).

Unbreak the build with Clang on architectures where JACK uses non-packed
data structures, like arm64 or powerpc. The alignment errors are exposed
there because:
 * The non-packed data structures require 8 byte alignment.
 * alignas() is not allowed to weaken alignment requirements to 4 bytes.
 * Clang enforces this according to standard, GCC ignores it.

Use an additional alignas() specifier to let the compiler choose between
minimum alignment (packed) and "natural" alignment (non-packed). This is
both standard c++11 and compatible with older GCC, which does not
propagate alignment requirements of packed substructures properly.

common/JackAtomicArrayState.h

@@ -122,7 +122,7 @@ class JackAtomicArrayState
         // fState[2] ==> request
 
         T fState[3];
-        alignas(UInt32) volatile AtomicArrayCounter fCounter;
+        alignas(UInt32) alignas(AtomicArrayCounter) volatile AtomicArrayCounter fCounter;
 
         UInt32 WriteNextStateStartAux(int state, bool* result)
         {

common/JackAtomicState.h

@@ -94,7 +94,7 @@ class JackAtomicState
     protected:
 
         T fState[2];
-        alignas(UInt32) volatile AtomicCounter fCounter;
+        alignas(UInt32) alignas(AtomicCounter) volatile AtomicCounter fCounter;
         SInt32 fCallWriteCounter;
 
         UInt32 WriteNextStateStartAux()

common/JackConnectionManager.h

@@ -417,7 +417,7 @@ class SERVER_EXPORT JackConnectionManager
         JackFixedArray1<PORT_NUM_FOR_CLIENT> fInputPort[CLIENT_NUM];	/*! Table of input port per refnum : to find a refnum for a given port */
         JackFixedArray<PORT_NUM_FOR_CLIENT> fOutputPort[CLIENT_NUM];	/*! Table of output port per refnum : to find a refnum for a given port */
         JackFixedMatrix<CLIENT_NUM> fConnectionRef;						/*! Table of port connections by (refnum , refnum) */
-        alignas(UInt32) JackActivationCount fInputCounter[CLIENT_NUM];	/*! Activation counter per refnum */
+        alignas(UInt32) alignas(JackActivationCount) JackActivationCount fInputCounter[CLIENT_NUM];	/*! Activation counter per refnum */
         JackLoopFeedback<CONNECTION_NUM_FOR_PORT> fLoopFeedback;		/*! Loop feedback connections */
 
         bool IsLoopPathAux(int ref1, int ref2) const;

common/JackEngineControl.h

@@ -64,7 +64,7 @@ struct SERVER_EXPORT JackEngineControl : public JackShmMem
     int fClientPriority;
     int fMaxClientPriority;
     char fServerName[JACK_SERVER_NAME_SIZE+1];
-    alignas(UInt32) JackTransportEngine fTransport;
+    alignas(UInt32) alignas(JackTransportEngine) JackTransportEngine fTransport;
     jack_timer_type_t fClockSource;
     int fDriverNum;
     bool fVerbose;
@@ -86,7 +86,7 @@ struct SERVER_EXPORT JackEngineControl : public JackShmMem
     UInt64 fConstraint;
 
     // Timer
-    alignas(UInt32) JackFrameTimer fFrameTimer;
+    alignas(UInt32) alignas(JackFrameTimer) JackFrameTimer fFrameTimer;
 
 #ifdef JACK_MONITOR
     JackEngineProfiling fProfiler;