util: Use unique type for QemuRecMutex in thread-posix.h

We will shortly convert lockable.h to _Generic, and we cannot
have two compatible types in the same expansion.  Wrap QemuMutex
in a struct, and unwrap in qemu-thread-posix.c.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210614233143.1221879-6-richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qemu/thread-posix.h

@@ -4,8 +4,6 @@
 #include <pthread.h>
 #include <semaphore.h>
 
-typedef QemuMutex QemuRecMutex;
-
 struct QemuMutex {
     pthread_mutex_t lock;
 #ifdef CONFIG_DEBUG_MUTEX
@@ -15,6 +13,14 @@ struct QemuMutex {
     bool initialized;
 };
 
+/*
+ * QemuRecMutex cannot be a typedef of QemuMutex lest we have two
+ * compatible cases in _Generic.  See qemu/lockable.h.
+ */
+typedef struct QemuRecMutex {
+    QemuMutex m;
+} QemuRecMutex;
+
 struct QemuCond {
     pthread_cond_t cond;
     bool initialized;

util/qemu-thread-posix.c

@@ -116,32 +116,32 @@ void qemu_rec_mutex_init(QemuRecMutex *mutex)
 
     pthread_mutexattr_init(&attr);
     pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
-    err = pthread_mutex_init(&mutex->lock, &attr);
+    err = pthread_mutex_init(&mutex->m.lock, &attr);
     pthread_mutexattr_destroy(&attr);
     if (err) {
         error_exit(err, __func__);
     }
-    mutex->initialized = true;
+    mutex->m.initialized = true;
 }
 
 void qemu_rec_mutex_destroy(QemuRecMutex *mutex)
 {
-    qemu_mutex_destroy(mutex);
+    qemu_mutex_destroy(&mutex->m);
 }
 
 void qemu_rec_mutex_lock_impl(QemuRecMutex *mutex, const char *file, int line)
 {
-    qemu_mutex_lock_impl(mutex, file, line);
+    qemu_mutex_lock_impl(&mutex->m, file, line);
 }
 
 int qemu_rec_mutex_trylock_impl(QemuRecMutex *mutex, const char *file, int line)
 {
-    return qemu_mutex_trylock_impl(mutex, file, line);
+    return qemu_mutex_trylock_impl(&mutex->m, file, line);
 }
 
 void qemu_rec_mutex_unlock_impl(QemuRecMutex *mutex, const char *file, int line)
 {
-    qemu_mutex_unlock_impl(mutex, file, line);
+    qemu_mutex_unlock_impl(&mutex->m, file, line);
 }
 
 void qemu_cond_init(QemuCond *cond)