patch from upstream https://github.com/NetHack/NetHack/commit/2445b97
fix with musl/gcc
https://github.com/NetHack/NetHack/issues/1530
https://bugs.gentoo.org/975067
--- a/sys/unix/hints/linux.500
+++ b/sys/unix/hints/linux.500
@@ -197,7 +197,10 @@ ifeq "$(CCISCLANG)" "1"
 # clang-specific ends
 else
 # gcc-specific starts
+ifndef MUSL
+# __sighandler_t does not exist in musl
 LIBCFLAGS+=-DSIG_RET_TYPE=__sighandler_t
+endif
 # gcc-specific ends
 endif