Adds genapply patch for 9.6

GenApply suffers from having GHC pollute its defines.

Author: angerman

overlays/bootstrap.nix

@@ -298,7 +298,8 @@ in {
                 # this one is to allow linking extra symbols from iserv.
                 ++ final.lib.optional (versionAtLeast "9.6.1"  && versionLessThan"9.10" && final.stdenv.targetPlatform.isAndroid) ./patches/ghc/iserv-syms.patch
                 ++ final.lib.optional (versionAtLeast "9.4"                             && final.stdenv.targetPlatform.isWindows) ./patches/ghc/ghc-9.6-fix-code-symbol-jumps.patch
-                ++ final.lib.optional (versionAtLeast "9.6.3"  && versionLessThan "9.10" && final.stdenv.targetPlatform.isAndroid) ./patches/ghc/ghc-9.6-iog.patch
+                ++ final.lib.optional (versionAtLeast "9.6.3"  && versionLessThan "9.10" && final.stdenv.targetPlatform.isAndroid) ./patches/ghc/ghc-9.6-iog.patch                                                                       ./patches/ghc/iserv-syms.patch
+                ++ final.lib.optional (versionAtLeast "9.6"    && versionLessThan "9.12" && final.stdenv.targetPlatform.is32bit) ./patches/ghc/ghc-9.6-genapply-cross-arch.patch
                 ;
         in ({
             ghc865 = final.callPackage ../compiler/ghc (traceWarnOld "8.6" {

overlays/patches/ghc/ghc-9.6-genapply-cross-arch.patch

@@ -0,0 +1,35 @@
+diff --git a/utils/genapply/Main.hs b/utils/genapply/Main.hs
+index 74351ee..8a6513c 100644
+--- a/utils/genapply/Main.hs
++++ b/utils/genapply/Main.hs
+@@ -12,6 +12,17 @@
+ -- for details
+ module Main(main) where
+ 
++-- GHC will helpfully pass
++-- -Dlinux_BUILD_OS -Dx86_64_BUILD_ARCH -Dlinux_HOST_OS -Dx86_64_HOST_ARCH -D__GLASGOW_HASKELL_TH__ -D__SSE__ -D__SSE2__ '-D__IO_MANAGER_MIO__=1'
++-- to cc -E when running the CPP phase. :-/ So we have to undefine them.
++#if defined(linux_BUILD_OS) || defined(x86_64_BUILD_ARCH) || defined(linux_HOST_OS) || defined(x86_64_HOST_ARCH)
++#warning "Undefining macros that GHC passes to CPP"
++#undef linux_BUILD_OS
++#undef x86_64_BUILD_ARCH
++#undef linux_HOST_OS
++#undef x86_64_HOST_ARCH
++#endif
++
+ -- Note [Genapply target as host for RTS macros]
+ -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ -- We improperly include *HOST* macros for our target...
+@@ -957,6 +968,12 @@ main = do
+                 text "// DO NOT EDIT!",
+                 text "// Automatically generated by utils/genapply/Main.hs",
+                 text "",
++                text "// DEBUG: SIZEOF_VOID_P " <> int SIZEOF_VOID_P,
++                text "// DEBUG: HOST_ARCH " <> text HOST_ARCH,
++                text "// DEBUG: HOST_OS " <> text HOST_OS,
++                text "// DEBUG: BUILD_ARCH " <> text BUILD_ARCH,
++                text "// DEBUG: BUILD_OS " <> text BUILD_OS,
++                text "",
+                 text "#include \"Cmm.h\"",
+                 text "#include \"AutoApply.h\"",
+                 text "#if !defined(UnregisterisedCompiler)",