Disable recursive interceptors in signal(3)/MSan

[krytarowski]

Summary

signal(3) on NetBSD calls internally sigaction(2).

Without disabling the recursive interceptor, there are
false positives about uninitialized memory reads inside libc.

This change fixes execution of such programs as sh(1) and
vmstat(1) in the NetBSD userland.

Sponsored by <The NetBSD Foundation>

[krytarowski]

ping?

lib/msan/msan_interceptors.cc

static int sigaction_impl(int signo, const __sanitizer_sigaction *act,
                           __sanitizer_sigaction *oldact);
 
 #define SIGNAL_INTERCEPTOR_SIGACTION_IMPL(signo, act, oldact) \
   { return sigaction_impl(signo, act, oldact); }
 
 #define SIGNAL_INTERCEPTOR_SIGNAL_IMPL(func, signo, handler) \
   {                                                          \
     handler = signal_impl(signo, handler);                   \
+    InterceptorScope interceptor_scope;                      \
     return REAL(func)(signo, handler);                       \
   }
 
 #include "sanitizer_common/sanitizer_signal_interceptors.inc"
 
 static int sigaction_impl(int signo, const __sanitizer_sigaction *act,
                           __sanitizer_sigaction *oldact) {
   ENSURE_MSAN_INITED();