<Make> Add hard links for toolchain

- These are default links added for first time cloning
- For people who wish to push to toolchain repos, use git ssh
  But later, run: `git update-index --skip-worktree mk/tc_get.mk`
  to avoid accidental pushes

mk/tc_get.mk

@@ -15,9 +15,9 @@ T_ALLOWLIST	+= get_all_tc get_avr_tc get_arm_tc get_riscv_tc
 # GIT REPO RECOMMENDED
 # Provide git repo path for toolchains for better experience
 ESIZE_REPO	:= https://github.com/VisorFolks/cc_elf_size.git
-AVR_TC_REPO	?=
-RISC_V_TC_REPO	?=
-ARM_TC_REPO	?=
+AVR_TC_REPO	?= https://github.com/VisorFolks/avr-toolchain
+RISC_V_TC_REPO	?= https://github.com/VisorFolks/risc-v-toolchain
+ARM_TC_REPO	?= https://github.com/VisorFolks/arm-toolchain
 
 get_all_tc: --tc_clear get_avr_tc get_arm_tc get_riscv_tc