icecc-toolchain: Disable caret workaround

icecc-toolchain: Disable caret workaround

Icecream has a behavior that causes it to recompile files locally if gcc
generates any warnings or errors. The reason for this is that GCC tries
to re-read the input file in order to display the offending line with a
caret below it, which doesn't work in the remote chroot.

Default to disabling this this workaround and add
-fno-diagnostics-show-caret to the GCC flags so that errors and warnings
generated by GCC do not show erroneous results. Users can override this
default in the SDK by defining ICECC_CARET_WORKAROUND="1" either before
or after sourcing the SDK environment.

(From OE-Core rev: 8933c2b5cfa59f2289c574e196f945556790c7c1)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>