signal.c: save the original sighandlers for fatal signals

On Android, a signal handler that is not SIG_DFL is set by default for
SIGSEGV.  Ruby's install_sighandler inserts Ruby's handler only when the
signal has no handler, so it does not insert Ruby's SEGV report handler,
which caused some test failures.

This changeset forces to install Ruby's handler for some fatal signals
(sigbus, sigsegv, and sigill).  They keep the original handlers, and
call them when the interpreter receives the signals.

1 files changed, 3 insertions, 1 deletions

diff --git a/error.c b/error.c
index 56ea9ae084..f8d2545fa6 100644
--- a/error.c
+++ b/error.c
@@ -599,7 +599,7 @@ rb_bug(const char *fmt, ...)
 }
 
 void
-rb_bug_for_fatal_signal(const void *ctx, const char *fmt, ...)
+rb_bug_for_fatal_signal(RETSIGTYPE (*default_sighandler)(int), int sig, const void *ctx, const char *fmt, ...)
 {
     const char *file = NULL;
     int line = 0;
@@ -610,6 +610,8 @@ rb_bug_for_fatal_signal(const void *ctx, const char *fmt, ...)
 
     report_bug(file, line, fmt, ctx);
 
+    if (default_sighandler) default_sighandler(sig);
+
     die();
 }