Fix struct sigevent decoding for musl

Do not rely on "struct sigevent.__pad" being located at the same address
as "struct sigevent.sigev_notify_thread_id", it's not the case with musl
libc.  Do not rely on struct sigevent definition at all to access
sigev_notify_thread_id.

* configure.ac (AC_CHECK_MEMBERS): Remove struct sigevent._sigev_un._pad
and struct sigevent.__pad.
* sigevent.h: New file.
* Makefile.am (strace_SOURCES): Add it.
* print_sigevent.c: Include it.
* print_sigevent.c (struct_sigevent): Remove.
(print_sigevent): Update all struct_sigevent users.
* tests/timer_create.c: Include "sigevent.h".
(main): Use struct_sigevent instead of struct sigevent,
all struct sigevent clients changed.
diff --git a/sigevent.h b/sigevent.h
new file mode 100644
index 0000000..6b3bacf
--- /dev/null
+++ b/sigevent.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2016 Dmitry V. Levin <ldv@altlinux.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef SIGEVENT_H_
+#define SIGEVENT_H_
+
+typedef struct {
+	union {
+		int sival_int;
+		unsigned long sival_ptr;
+	} sigev_value;
+	int sigev_signo;
+	int sigev_notify;
+	union {
+		int tid;
+		struct {
+			unsigned long function;
+			unsigned long attribute;
+		} sigev_thread;
+	} sigev_un;
+} struct_sigevent;
+
+#endif