thread/Posix{Mutex,Cond}: use "constexpr" only with glibc

NEWS

 ver 0.19.14 (not yet released)
+* fix build failures on non-glibc builds due to constexpr Mutex
 
 ver 0.19.13 (2016/02/23)
 * tags

src/thread/PosixCond.hxx

@@ -41,9 +41,13 @@ class PosixCond {
 	pthread_cond_t cond;
 
 public:
-#if defined(__NetBSD__) || defined(__BIONIC__)
-	/* NetBSD's PTHREAD_COND_INITIALIZER is not compatible with
-	   "constexpr" */
+#ifdef __GLIBC__
+	/* optimized constexpr constructor for pthread implementations
+	   that support it */
+	constexpr PosixCond():cond(PTHREAD_COND_INITIALIZER) {}
+#else
+	/* slow fallback for pthread implementations that are not
+	   compatible with "constexpr" */
 	PosixCond() {
 		pthread_cond_init(&cond, nullptr);
 	}
@@ -51,10 +55,6 @@ public:
 	~PosixCond() {
 		pthread_cond_destroy(&cond);
 	}
-#else
-	/* optimized constexpr constructor for sane POSIX
-	   implementations */
-	constexpr PosixCond():cond(PTHREAD_COND_INITIALIZER) {}
 #endif
 
 	PosixCond(const PosixCond &other) = delete;

src/thread/PosixMutex.hxx

@@ -41,9 +41,13 @@ class PosixMutex {
 	pthread_mutex_t mutex;
 
 public:
-#if defined(__NetBSD__) || defined(__BIONIC__)
-	/* NetBSD's PTHREAD_MUTEX_INITIALIZER is not compatible with
-	   "constexpr" */
+#ifdef __GLIBC__
+	/* optimized constexpr constructor for pthread implementations
+	   that support it */
+	constexpr PosixMutex():mutex(PTHREAD_MUTEX_INITIALIZER) {}
+#else
+	/* slow fallback for pthread implementations that are not
+	   compatible with "constexpr" */
 	PosixMutex() {
 		pthread_mutex_init(&mutex, nullptr);
 	}
@@ -51,10 +55,6 @@ public:
 	~PosixMutex() {
 		pthread_mutex_destroy(&mutex);
 	}
-#else
-	/* optimized constexpr constructor for sane POSIX
-	   implementations */
-	constexpr PosixMutex():mutex(PTHREAD_MUTEX_INITIALIZER) {}
 #endif
 
 	PosixMutex(const PosixMutex &other) = delete;