lld21/llvm-native: pin cross tblgen to version-matched redoxer toolchain

Cross-building lld/llvm needs a HOST-runnable llvm-tblgen to generate the
Options.inc opt-parser sources, and it must match the LLVM 21 source tree.
Both recipes referenced ${COOKBOOK_HOST_SYSROOT}/bin/llvm-tblgen, but the
cookbook does not export COOKBOOK_HOST_SYSROOT, so the path collapsed to the
host /bin/llvm-tblgen. On a rolling distro that is now LLVM 22, whose
-gen-opt-parser-defs backend requires a 'SubCommand' TableGen class absent
from LLVM 21's OptParser.td:

    error: The class 'SubCommand' is not defined

Default COOKBOOK_HOST_SYSROOT to the redoxer toolchain (host-runnable LLVM
21.1.2 llvm-/clang-tblgen), exactly as the sibling clang21 recipe already
does. Fixes the full-target build reaching mesa's LLVM build-deps.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

local/recipes/dev/llvm-native/recipe.toml

@@ -23,6 +23,14 @@ case "${ARCH}" in
     riscv64gc) LLVM_TARGETS_TO_BUILD="RISCV";;
 esac
 
+# The *-tblgen references below must be VERSION-MATCHED to this LLVM source
+# tree. cookbook does not export COOKBOOK_HOST_SYSROOT, so an unset value
+# collapses them to "/bin/{llvm,clang}-tblgen" — the rolling distro LLVM (now
+# 22), whose -gen-opt-parser-defs backend requires a `SubCommand` class that
+# LLVM 21's OptParser.td does not define. Point at the redoxer toolchain's
+# host-runnable LLVM 21.1.2 tblgen, matching the clang21/lld21 recipes.
+export COOKBOOK_HOST_SYSROOT="${COOKBOOK_HOST_SYSROOT:-${HOME}/.redoxer/${TARGET}/toolchain}"
+
 COOKBOOK_CMAKE_FLAGS+=(
     -DLLVM_ENABLE_PROJECTS="clang;lld"
     -DLLVM_BUILD_LLVM_DYLIB=On

recipes/dev/lld21/recipe.toml

@@ -24,6 +24,16 @@ generate_cookbook_cmake_file "$COOKBOOK_HOST_TARGET" "" "$COOKBOOK_TOOLCHAIN" na
 if [ "$TARGET" = "$COOKBOOK_HOST_TARGET" ]; then
 COOKBOOK_CMAKE_FLAGS+=( -DLLVM_TABLEGEN_EXE=${COOKBOOK_TOOLCHAIN}/bin/llvm-tblgen )
 else
+# Cross-building lld needs a HOST-runnable llvm-tblgen to generate the
+# Options.inc sources, and it MUST be version-matched to the LLVM 21 source
+# tree: the host's /bin/llvm-tblgen tracks the rolling distro LLVM (now 22),
+# whose -gen-opt-parser-defs backend requires a `SubCommand` class that LLVM
+# 21's OptParser.td does not define ("error: The class 'SubCommand' is not
+# defined"). cookbook does not export COOKBOOK_HOST_SYSROOT, so the reference
+# below collapsed to "/bin/llvm-tblgen" (the mismatched host tool). The
+# redoxer toolchain ships a host-runnable LLVM 21.1.2 llvm-tblgen; point at it
+# exactly as the sibling clang21 recipe does.
+export COOKBOOK_HOST_SYSROOT="${COOKBOOK_HOST_SYSROOT:-${HOME}/.redoxer/${TARGET}/toolchain}"
 COOKBOOK_CMAKE_FLAGS+=( -DLLVM_TABLEGEN_EXE=${COOKBOOK_HOST_SYSROOT}/bin/llvm-tblgen )
 fi