use `defconfig` for ct-ng, minimizing the config

[Emilgardis]

We should switch to using a minimal .config for our crosstool-ng targets.

A way to do this is with ct-ng savedefconfig and ct-ng olddefconfig

An issue with this is that it doesn't seem to respect comp lib versions, need to solve that somehow.

[Emilgardis]

for example

CT_CONFIG_VERSION="4"
CT_PREFIX_DIR="/x-tools/${CT_TARGET}"
CT_ARCH_ARM=y
CT_USE_MIRRORS=y
CT_ARCH_ARCH="armv6"
CT_ARCH_FPU="vfp"
CT_ARCH_FLOAT_HW=y
CT_KERNEL_LINUX=y
CT_LINUX_V_4_19=y
CT_BINUTILS_V_2_32=y
CT_GLIBC_V_2_31=y
CT_GCC_V_8=y
CT_CC_LANG_CXX=y
CT_GETTEXT_V_0_19_8_1=y
CT_GMP_V_6_1=y
CT_ISL_V_0_20=y
CT_LIBICONV_V_1_15=y
CT_NCURSES_V_6_1=y
CT_ZLIB_V_1_2_13=y
CT_ZLIB_MIRRORS="https://github.com/madler/zlib/releases/download/v${CT_ZLIB_VERSION}/ https://www.zlib.net/"

expands to using zlib 1.2.12 using ct-ng 1.25.0