add fix-build-using-unregisterised-v8.6.patch from Debian

fix-build-using-unregisterised-v8.6.patch

@@ -0,0 +1,31 @@
+Description: Allow unregisterised ghc-8.6 to build newer GHC
+ Commit af9b744bbf1 introduced a regression stopping existing unregisterised
+ compilers from being able to compile newer versions of GHC. The problem is
+ that the bootstrap compiler uses the newer `includes/stg/MiscClosures.h` file
+ where some defines have been renamed, resulting in the following error:
+.
+ error: ‘stg_atomicModifyMutVarzh’ undeclared (first use in this function); did you mean ‘stg_atomicModifyMutVar2zh’?
+.
+ For more information, see https://gitlab.haskell.org/ghc/ghc/issues/17111.
+.
+ This patch can be removed, once ghc-8.6 is no longer the bootstrap compiler.
+Author: Ilias Tsitsimpis <iliastsi@debian.org>
+Bug: https://gitlab.haskell.org/ghc/ghc/issues/17111
+
+Index: b/includes/stg/MiscClosures.h
+===================================================================
+--- a/includes/stg/MiscClosures.h
++++ b/includes/stg/MiscClosures.h
+@@ -390,8 +390,12 @@ RTS_FUN_DECL(stg_copySmallMutableArrayzh
+ RTS_FUN_DECL(stg_casSmallArrayzh);
+ 
+ RTS_FUN_DECL(stg_newMutVarzh);
++#if __GLASGOW_HASKELL__ < 808
++RTS_FUN_DECL(stg_atomicModifyMutVarzh);
++#else
+ RTS_FUN_DECL(stg_atomicModifyMutVar2zh);
+ RTS_FUN_DECL(stg_atomicModifyMutVarzuzh);
++#endif
+ RTS_FUN_DECL(stg_casMutVarzh);
+ 
+ RTS_FUN_DECL(stg_isEmptyMVarzh);

ghc.spec

@@ -77,6 +77,7 @@ Patch12: ghc-armv7-VFPv3D16--NEON.patch
 # for unregisterized (s390x)
 # https://ghc.haskell.org/trac/ghc/ticket/15689
 Patch15: ghc-warnings.mk-CC-Wall.patch
+Patch16: fix-build-using-unregisterised-v8.6.patch
 
 # bigendian (s390x and ppc64)
 # https://gitlab.haskell.org/ghc/ghc/issues/15411
@@ -327,6 +328,7 @@ rm -r libffi-tarballs
 
 %ifarch %{ghc_unregisterized_arches}
 %patch15 -p1 -b .orig
+%patch16 -p1 -b .orig
 %endif
 
 # bigendian