relevant bug:
https://sourceware.org/bugzilla/show_bug.cgi?id=23616

diff --git a/gdbsupport/signals.cc b/gdbsupport/signals.cc
index 485e0f0..ab8d454 100644
--- a/gdbsupport/signals.cc
+++ b/gdbsupport/signals.cc
@@ -31,6 +31,13 @@ struct gdbarch;
    _available_ realtime signal, not the lowest supported; glibc takes
    several for its own use.  */
 
+#ifndef __SIGRTMIN
+# define __SIGRTMIN 32
+#endif
+#ifndef __SIGRTMAX
+# define __SIGRTMAX _NSIG
+#endif
+
 #ifndef REALTIME_LO
 # if defined(__SIGRTMIN)
 #  define REALTIME_LO __SIGRTMIN