linux-user: avoid using glibc internals in _syscall5 and in definition of target_sigevent struct

Use the public sigset_t instead of the glibc specific internal
__sigset_t in _syscall.

Calculate the sigevent pad size is calculated in similar way as kernel
does it instead of using glibc internal field _pad.

This is needed for building with musl libc.
Signed-off-by: NNatanael Copa <ncopa@alpinelinux.org>
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>

linux-user/syscall.c

@@ -411,7 +411,7 @@ static int sys_inotify_init1(int flags)
 #endif
 #define __NR_sys_ppoll __NR_ppoll
 _syscall5(int, sys_ppoll, struct pollfd *, fds, nfds_t, nfds,
-          struct timespec *, timeout, const __sigset_t *, sigmask,
+          struct timespec *, timeout, const sigset_t *, sigmask,
           size_t, sigsetsize)
 #endif
 

linux-user/syscall_defs.h

@@ -2552,12 +2552,26 @@ struct target_timer_t {
     abi_ulong ptr;
 };
 
+#define TARGET_SIGEV_MAX_SIZE 64
+
+/* This is architecture-specific but most architectures use the default */
+#ifdef TARGET_MIPS
+#define TARGET_SIGEV_PREAMBLE_SIZE (sizeof(int32_t) * 2 + sizeof(abi_long))
+#else
+#define TARGET_SIGEV_PREAMBLE_SIZE (sizeof(int32_t) * 2 \
+                                    + sizeof(target_sigval_t))
+#endif
+
+#define TARGET_SIGEV_PAD_SIZE ((TARGET_SIGEV_MAX_SIZE \
+                                - TARGET_SIGEV_PREAMBLE_SIZE) \
+                               / sizeof(int32_t))
+
 struct target_sigevent {
     target_sigval_t sigev_value;
     int32_t sigev_signo;
     int32_t sigev_notify;
     union {
-        int32_t _pad[ARRAY_SIZE(((struct sigevent *)0)->_sigev_un._pad)];
+        int32_t _pad[TARGET_SIGEV_PAD_SIZE];
         int32_t _tid;
 
         struct {