Question

>>> toolchain-external-custom  Configuring
RPC support not available in C library, please disable BR2_TOOLCHAIN_EXTERNAL_INET_RPC
make[1]: *** [package/pkg-generic.mk:283: /[...]/buildroot/output/xxx/build/toolchain-external-custom/.stamp_configured] Error 1

Answer

# BR2_TOOLCHAIN_EXTERNAL_INET_RPC is not set