[sanitizer] Forward declaration of __sanitizer_sigaction without signal interceptors

llvm-svn: 317870

compiler-rt/lib/sanitizer_common/sanitizer_signal_interceptors.inc

@@ -62,6 +62,9 @@ int real_sigaction(int signum, const void *act, void *oldact) {
 #define INIT_SIGNAL
 #define INIT_SIGACTION
 // We need to have defined REAL(sigaction) on other systems.
+namespace __sanitizer {
+struct __sanitizer_sigaction;
+}
 DEFINE_REAL(int, sigaction, int signum, const __sanitizer_sigaction *act,
             __sanitizer_sigaction *oldact)
 #endif  // SANITIZER_INTERCEPT_SIGNAL_AND_SIGACTION