games-roguelike/nethack: don't redefine warn_unused_result

Apply patch that should land in NetHack 3.6.7. No revbump as fixes build
failure.

Closes: https://bugs.gentoo.org/830556
Signed-off-by: Matthew Smith <matthew@gentoo.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/games-roguelike/nethack/files/nethack-3.6.6-wunused-result.patch b/games-roguelike/nethack/files/nethack-3.6.6-wunused-result.patch
new file mode 100644
index 000000000000..e26d1190fda3
--- /dev/null
+++ b/games-roguelike/nethack/files/nethack-3.6.6-wunused-result.patch
@@ -0,0 +1,37 @@
+From 1cb5dc04605daa45f1c6a647c17442ed7ff2fe4e Mon Sep 17 00:00:00 2001
+From: nhmall <nhmall@nethack.org>
+Date: Tue, 4 Jan 2022 08:24:08 -0500
+Subject: [PATCH] work around ubuntu 20.10 build issue
+
+NetHack was trying to suppress warn_unused_result
+in include/tradstdc.h, by defining warn_unused_result
+to an empty string. That began causing a build error
+in a system-supplied header file cdefs.h
+when using 20.10 ubuntu impish.
+
+Try skipping that in tradstdc.h for any linux, unless
+the NetHack build defines GCC_URWARN to force it into
+play.
+---
+ include/tradstdc.h | 2 ++
+ 1 file changed, 2 insertions(+)
+
+diff --git a/include/tradstdc.h b/include/tradstdc.h
+index 09decb4b15..8c33d55e0a 100644
+--- a/include/tradstdc.h
++++ b/include/tradstdc.h
+@@ -405,12 +405,14 @@ typedef genericptr genericptr_t; /* (void *) or (char *) */
+ #if __GNUC__ >= 3
+ #define UNUSED __attribute__((unused))
+ #define NORETURN __attribute__((noreturn))
++#if !defined(__linux__) || defined(GCC_URWARN)
+ /* disable gcc's __attribute__((__warn_unused_result__)) since explicitly
+    discarding the result by casting to (void) is not accepted as a 'use' */
+ #define __warn_unused_result__ /*empty*/
+ #define warn_unused_result /*empty*/
+ #endif
+ #endif
++#endif
+ 
+ #ifndef PRINTF_F
+ #define PRINTF_F(f, v)