https://bugs.gentoo.org/639562

--- emacs-18.59-orig/src/ChangeLog
+++ emacs-18.59/src/ChangeLog
@@ -1,3 +1,8 @@
+2017-12-07  Ulrich Mueller  <ulm@gentoo.org>
+
+	* s-linux.h (SIGSYS): Don't redefine. Fixes compilation with
+	glibc-2.26 headers.
+
 2015-12-20  Ulrich Mueller  <ulm@gentoo.org>
 
 	* s-linux.h (SYSTEM_MALLOC): Define. Fixes hanging at runtime
--- emacs-18.59-orig/src/s-linux.h
+++ emacs-18.59/src/s-linux.h
@@ -225,8 +225,6 @@
 #define MAXNAMLEN NAME_MAX	/* missing SYSV-ism */
 #endif
 
-#undef SIGSYS
-#define SIGSYS SIGUNUSED	/* rename to harmless work-alike */
 #define VSWTCH VSWTC		/* mis-spelling in termios.h? */
 
 /* we have non-standard standard I/O (iostream) ... */