Restore SIGFPE handler after initializing PL/Perl.

Perl, for some unaccountable reason, believes it's a good idea to reset
SIGFPE handling to SIG_IGN.  Which wouldn't be a good idea even if it
worked; but on some platforms (Linux at least) it doesn't work at all,
instead resulting in forced process termination if the signal occurs.
Given the lack of other complaints, it seems safe to assume that Perl
never actually provokes SIGFPE and so there is no value in the setting
anyway.  Hence, reset it to our normal handler after initializing Perl.

Report, analysis and patch by Andres Freund.

Author: tglsfdc

src/pl/plperl/plperl.c

@@ -24,11 +24,13 @@
 #include "commands/trigger.h"
 #include "executor/spi.h"
 #include "funcapi.h"
+#include "libpq/pqsignal.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "parser/parse_type.h"
 #include "storage/ipc.h"
+#include "tcop/tcopprot.h"
 #include "utils/builtins.h"
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
@@ -742,6 +744,18 @@ plperl_init_interp(void)
 			char	   *dummy_env[1] = {NULL};
 
 			PERL_SYS_INIT3(&nargs, (char ***) &embedding, (char ***) &dummy_env);
+
+			/*
+			 * For unclear reasons, PERL_SYS_INIT3 sets the SIGFPE handler to
+			 * SIG_IGN.  Aside from being extremely unfriendly behavior for a
+			 * library, this is dumb on the grounds that the results of a
+			 * SIGFPE in this state are undefined according to POSIX, and in
+			 * fact you get a forced process kill at least on Linux.  Hence,
+			 * restore the SIGFPE handler to the backend's standard setting.
+			 * (See Perl bug 114574 for more information.)
+			 */
+			pqsignal(SIGFPE, FloatExceptionHandler);
+
 			perl_sys_init_done = 1;
 			/* quiet warning if PERL_SYS_INIT3 doesn't use the third argument */
 			dummy_env[0] = NULL;