boost-build: fix overriding target when llvm

pkgs/development/tools/boost-build/default.nix

@@ -33,7 +33,8 @@ stdenv.mkDerivation {
     sourceRoot="$sourceRoot/tools/build"
   '';
 
-  patches = useBoost.boostBuildPatches or [];
+  patches = useBoost.boostBuildPatches or []
+    ++ lib.optional (useBoost ? version && lib.versionAtLeast useBoost.version "1.81") ./fix-clang-target.patch;
 
   # Upstream defaults to gcc on darwin, but we use clang.
   postPatch = ''

pkgs/development/tools/boost-build/fix-clang-target.patch

@@ -0,0 +1,14 @@
+--- a/src/tools/clang.jam	2024-07-25 10:38:16.278401900 -0700
++++ b/src/tools/clang.jam	2024-07-25 10:38:52.659750666 -0700
+@@ -90,11 +90,6 @@
+                 case x86-64 : arch = x86_64 ;
+                 case x86-32 : arch = i386 ;
+             }
+-
+-            toolset.flags $(toolset)
+-                OPTIONS $(condition)/<target-os>$(target-os)/<architecture>$(_architecture_)/<address-model>$(_address-model_)
+-                : "--target=$(arch)-$(vendor-sys)"
+-                : unchecked ;
+         }
+     }
+ }