Simplify kernel build recipe

Move a bunch of options from recipe.toml to Cargo.toml and the target specs. Also make rustc invoke the linker rather than having the recipe run it. And finally switch the linker to the lld bundled with rustc.

Depends on kernel!253 (merged)

recipes/kernel/recipe.toml

@@ -7,22 +7,15 @@ script = """
 export RUST_TARGET_PATH="${COOKBOOK_SOURCE}/targets"
 ARCH="$(echo "${TARGET}" | cut -d - -f1)"
 cargo rustc \
-	--lib \
+	--bin kernel \
 	--manifest-path "${COOKBOOK_SOURCE}/Cargo.toml" \
 	--target "${COOKBOOK_SOURCE}/targets/${ARCH}-unknown-kernel.json" \
 	--release \
 	-Z build-std=core,alloc \
 	-- \
 	-C soft-float \
-	-C debuginfo=2 \
-	-C lto \
-	--emit link="${PWD}/libkernel.a"
-"${TARGET}-ld" \
-	--gc-sections \
-	-z max-page-size=0x1000 \
-	-T "${COOKBOOK_SOURCE}/linkers/${ARCH}.ld" \
-	-o kernel.all \
-	libkernel.a
+	-C link-arg=-T -Clink-arg="${COOKBOOK_SOURCE}/linkers/${ARCH}.ld" \
+	--emit link="${PWD}/kernel.all"
 "${TARGET}-objcopy" \
 	--only-keep-debug \
 	kernel.all \