posix: mqueue: pop mode as int with va_arg()

There was some discussion about whether it was suitable to have
an architecture-specific workaround in mqueue.c after that
workaround was copied to a different source file in a PR.

The original issue was that newlib and picolibc declare mode_t
to be unsigned short instead of unsigned long when __svr4__
is not defined along with __sparc__. This is specifically
impactful, because va_arg() deals (mainly) with 32-bit and
64-bit values that are all naturally aligned to 4 bytes.

#if defined(__sparc__) && !defined(__sparc_v9__)
#ifdef __svr4__
typedef unsigned long __mode_t;
#else
typedef unsigned short __mode_t;
#endif

A uint16_t is naturally aligned to 2 bytes, so not only would
a 16-bit mode_t be corrupted, it would also generate a warning
with recent gcc versions which is promoted to error (rightfully
so) when run through CI.

mqueue.c:61:35: error: 'mode_t' {aka 'short unsigned int'} is
  promoted to 'int' when passed through '...' [-Werror]
   61 |                 mode = va_arg(va, mode_t);

Instead of using an architecture-specific workaround, simply
add a build assert that the size of mode_t is less than or
equal to the size of an int, and use an int to retrieve it
via va_arg().

Signed-off-by: Christopher Friedt <cfriedt@meta.com>

# Please enter the commit message for your changes. Lines starting
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#
# Date:      Fri Dec 29 10:06:44 2023 -0500
#
# On branch posix-mqueue-always-use-int-for-mode-t-va-arg
# Changes to be committed:
#	modified:   lib/posix/mqueue.c
#	modified:   tests/posix/common/testcase.yaml
#

lib/posix/mqueue.c

@@ -38,17 +38,6 @@ static int receive_message(mqueue_desc *mqd, char *msg_ptr, size_t msg_len,
 			   k_timeout_t timeout);
 static void remove_mq(mqueue_object *msg_queue);
 
-#if defined(__sparc__)
-/*
- * mode_t is defined as "unsigned short" on SPARC newlib. This type is promoted
- * to "int" when passed through '...' so we should pass the promoted type to
- * va_arg().
- */
-#define PROMOTED_MODE_T int
-#else
-#define PROMOTED_MODE_T mode_t
-#endif
-
 /**
  * @brief Open a message queue.
  *
@@ -69,7 +58,8 @@ mqd_t mq_open(const char *name, int oflags, ...)
 
 	va_start(va, oflags);
 	if ((oflags & O_CREAT) != 0) {
-		mode = va_arg(va, PROMOTED_MODE_T);
+		BUILD_ASSERT(sizeof(mode_t) <= sizeof(int));
+		mode = va_arg(va, unsigned int);
 		attrs = va_arg(va, struct mq_attr*);
 	}
 	va_end(va);

tests/posix/common/testcase.yaml

@@ -1,9 +1,6 @@
 common:
   filter: not (CONFIG_NATIVE_BUILD and CONFIG_EXTERNAL_LIBC)
-  # FIXME: qemu_leon3 is excluded because of the alignment-related failure
-  #        reported in the GitHub issue zephyrproject-rtos/zephyr#48992.
   platform_exclude:
-    - qemu_leon3
     - native_posix
     - native_posix_64
   tags: posix