[Android] bootslag:
Oh so what I did first was right. Also I found a file AndroidKernel.mk on my device's open source code (Android makefile to build kernel as a part of Android Build) I replaced /vendor/build/tasks/kernel.mk with that and included this on my BoardConfig.mk:

# Kernel
TARGET_PREBUILT_KERNEL := device/lenovo/YT3850M/prebuilt/kernel
PRODUCT_COPY_FILES += \
$(TARGET_PREBUILT_KERNEL):kernel

But as the build continued I got a new kind of error: packages/overlays/Lineage/accents/black/AndroidManifest.xml:25: error: Error: No resource found that matches the given name (at 'label' with value '@*lineageos.platform:string/accent_black').

[ 56% 43363/76120] AAPT2 compile /home/rh/lineage/out/target/common/obj/JAVA_LIBRARIES/libphotoviewe...ks/opt/photoviewer/res/values_strings.arsc.flat <- frameworks/opt/photoviewer/res/values/strings.xml
frameworks/opt/photoviewer/res/values/strings.xml:20: warn: multiple substitutions specified in non-positional format; did you mean to add the formatted="false" attribute?.
frameworks/opt/photoviewer/res/values/strings.xml:25: warn: multiple substitutions specified in non-positional format; did you mean to add the formatted="false" attribute?.
[ 60% 45712/76120] AAPT2 link /home/rh/lineage/out/target/product/YT3850M/obj/APPS/Bluetooth_intermediates/package-res.apk
packages/apps/Bluetooth/res/layout/bt_enabling_progress.xml:30: warn: generated id 'android:id/progress' for external package 'android'.
[ 60% 45768/76120] target R.java/Manifest.java: LineageBlackAccent (/home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/src/R.stamp)
FAILED: /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/src/R.stamp
/bin/bash -c "(rm -rf /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/src/R.stamp && mkdir -p /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/src/ ) && (mkdir -p /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/src ) && (mkdir -p /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/ ) && (ASAN_OPTIONS=detect_leaks=0 /home/rh/lineage/out/host/linux-x86/bin/aapt package -z --pseudo-localize -m -J /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/src -M packages/overlays/Lineage/accents/black/AndroidManifest.xml -P /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/public_resources.xml -S packages/overlays/Lineage/accents/black/res -I /home/rh/lineage/out/target/common/obj/APPS/framework-res_intermediates/package-export.apk -G /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/proguard_options --min-sdk-version 27 --target-sdk-version 27 --version-code 27 --version-name 8.1.0 --skip-symbols-without-default-localization ) && (for GENERATED_MANIFEST_FILE in \`find /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/src -name Manifest.java 2> /dev/null\`; do dir=\`awk '/package/{gsub(/\\./,\"/\",\$2);gsub(/;/,\"\",\$2);print \$2;exit}' \$GENERATED_MANIFEST_FILE\`; mkdir -p /home/rh/lineage/out/target/common/R/\$dir; prebuilts/build-tools/linux-x86/bin/acp -fp \$GENERATED_MANIFEST_FILE /home/rh/lineage/out/target/common/R/\$dir; done ) && (for GENERATED_R_FILE in \`find /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/src -name R.java 2> /dev/null\`; do dir=\`awk '/package/{gsub(/\\./,\"/\",\$2);gsub(/;/,\"\",\$2);print \$2;exit}' \$GENERATED_R_FILE\`; mkdir -p /home/rh/lineage/out/target/common/R/\$dir; prebuilts/build-tools/linux-x86/bin/acp -fp \$GENERATED_R_FILE /home/rh/lineage/out/target/common/R/\$dir || exit 31; prebuilts/build-tools/linux-x86/bin/acp -fp \$GENERATED_R_FILE /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/src/R.stamp || exit 32; done ) && (touch /home/rh/lineage/out/target/common/obj/APPS/LineageBlackAccent_intermediates/src/R.stamp )"
packages/overlays/Lineage/accents/black/AndroidManifest.xml:25: error: Error: No resource found that matches the given name (at 'label' with value '@*lineageos.platform:string/accent_black').

[ 60% 45772/76120] target R.java/Manifest.java: Email (/home/rh/lineage/out/target/common/obj/APPS/Email_intermediates/src/R.stamp)
ninja: build stopped: subcommand failed.
22:30:19 ninja failed with: exit status 1

#### failed to build some targets (30:42 (mm:ss)) ####

rh@inspiron:~/lineage$