CONFIG_DEBUG_SECTION_MISMATCH error : Get rid of it!
Kernel TC - TARGET_GCC_VERSION := 4.x
ROM TC - TARGET GCC_VERSION_EXP := 4.x
where x is the version that your ROM source is using.Generally most ROMs use 4.8 for kernel and 4.9 for the ROM as default.
You can still take a look at prebuilts/gcc/linux_x86/arm (arm64 for 64 bit devices)/*here* for the toolchain you want to use.
If you have any more queries,comment down below.