Disable regexp JIT by default.

Index: deps/v8/src/flags/flag-definitions.h
--- deps/v8/src/flags/flag-definitions.h.orig
+++ deps/v8/src/flags/flag-definitions.h
@@ -2835,7 +2835,13 @@ DEFINE_BOOL(serialization_statistics, false,
             "Collect statistics on serialized objects.")
 // Regexp
 DEFINE_BOOL(regexp_optimization, true, "generate optimized regexp code")
+#ifdef V8_OS_OPENBSD
+// OpenBSD: Irregexp JIT rewrites a C++ return address, which conflicts with
+// retguard. Use bytecode interpretation by default.
+DEFINE_BOOL(regexp_interpret_all, true, "interpret all regexp code")
+#else
 DEFINE_BOOL(regexp_interpret_all, false, "interpret all regexp code")
+#endif
 #ifdef V8_TARGET_BIG_ENDIAN
 #define REGEXP_PEEPHOLE_OPTIMIZATION_BOOL false
 #else
