zdb/ztest: use libspl backtrace for crashes

We can show much nicer backtraces these days, lets use them.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #16181

lib/libspl/assert.c

@@ -55,7 +55,7 @@
 #define	UNW_LOCAL_ONLY
 #include <libunwind.h>
 
-static inline void
+void
 libspl_dump_backtrace(void)
 {
 	unw_context_t uc;
@@ -85,7 +85,7 @@ libspl_dump_backtrace(void)
 #elif defined(HAVE_BACKTRACE)
 #include <execinfo.h>
 
-static inline void
+void
 libspl_dump_backtrace(void)
 {
 	void *btptrs[100];
@@ -97,7 +97,10 @@ libspl_dump_backtrace(void)
 	free(bt);
 }
 #else
-#define	libspl_dump_backtrace()
+void
+libspl_dump_backtrace(void)
+{
+}
 #endif
 
 #if defined(__APPLE__)

lib/libspl/include/assert.h

@@ -60,6 +60,8 @@ libspl_assert(const char *buf, const char *file, const char *func, int line)
 	return (0);
 }
 
+extern void libspl_dump_backtrace(void);
+
 #ifdef verify
 #undef verify
 #endif