arm-none-eabi-gcc broken with current link.x.in

[adamgreig]

In #207 we updated the linker script to fix #188 but unfortunately this seems to have broken arm-none-eabi-gcc, which can no longer link:

section .init LMA [0000000008001614,000000000800161f] overlaps section .rodata LMA [0000000008001614,00000000080017cf]

The exact problem is adding __extext here:
d5f2a94#diff-21b67a00d2a7d05c7aa7f0fe1a2f8adfR96

From the tests I just ran, removing this preserves rust-lld and arm-none-eabi-ld linkability, but fixes arm-none-eabi-gcc, so perhaps we should revert that change (and backport to 0.6.x)?

Possibly we should update the CI tests to run against arm-none-eabi-gcc as well as the current arm-none-eabi-ld and rust-lld.

[adamgreig]

Closing: gcc requires -nostartfiles and then does not mind this __extext, see #260 for further details. CI was updated to include arm-none-eabi-gcc in #262.