Cannot able to build

Hi, I followed the steps given below in the link

I have setup-ed build system as given below the link

While I was executing the step I ran into the Error

step
make -j $(nproc) kernel_menuconfig

Error

make[5]: Leaving directory '/home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0-initial/build-x86_64-pc-linux-gnu/fixincludes'
make[5]: Entering directory '/home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0-initial/build-x86_64-pc-linux-gnu/libcpp'
g++  -I/home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0/libcpp -I. -I/home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0/libcpp/../include -I/home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0/libcpp/include  -g -O2 -W -Wall -Wno-narrowing -Wwrite-strings -Wmissing-format-attribute -pedantic -Wno-long-long  -fno-exceptions -fno-rtti -I/home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0/libcpp -I. -I/home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0/libcpp/../include -I/home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0/libcpp/include   -c -o charset.o -MT charset.o -MMD -MP -MF .deps/charset.Tpo /home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0/libcpp/charset.c
In file included from /home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0/libcpp/charset.c:20:
./config.h:356:19: error: multiple types in one declaration
  356 | #define ptrdiff_t int
      |                   ^~~
./config.h:356:19: error: declaration does not declare anything [-fpermissive]
./config.h:356:19: error: multiple types in one declaration
  356 | #define ptrdiff_t int
      |                   ^~~
./config.h:356:19: error: declaration does not declare anything [-fpermissive]
make[5]: *** [Makefile:224: charset.o] Error 1
make[5]: Leaving directory '/home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0-initial/build-x86_64-pc-linux-gnu/libcpp'
make[4]: *** [Makefile:2729: all-build-libcpp] Error 2
make[4]: Leaving directory '/home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0-initial'
make[3]: *** [Makefile:37: /home/shouvik/Documents/openwrt/build_dir/toolchain-mips_24kc_gcc-8.4.0_musl/gcc-8.4.0-initial/.built] Error 2
make[3]: Leaving directory '/home/shouvik/Documents/openwrt/toolchain/gcc/initial'
time: toolchain/gcc/initial/compile#0.32#0.10#0.44
    ERROR: toolchain/gcc/initial failed to build.
make[2]: *** [toolchain/Makefile:97: toolchain/gcc/initial/compile] Error 1
make[2]: Leaving directory '/home/shouvik/Documents/openwrt'
make[1]: *** [toolchain/Makefile:93: /home/shouvik/Documents/openwrt/staging_dir/toolchain-mips_24kc_gcc-8.4.0_musl/stamp/.toolchain_compile] Error 2
make[1]: Leaving directory '/home/shouvik/Documents/openwrt'
make: *** [/home/shouvik/Documents/openwrt/include/toplevel.mk:230: world] Error 2

OS

Distributor ID: Ubuntu
Description: Ubuntu 20.04.4 LTS
Release: 20.04
Codename: focal

Can you help me out, with the error.