fix: disable `-Wsign-compare`

The `-Wextra` flag was enabled in the parent `BUILD.gn`, which causes
`dtc` to inherit the `-Wextra` flag and fail to compile with
`-Wsign-compare` errors.

Change-Id: I3ecd8871bda1620d5bf741814f4cf342ac22ed36
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
1 file changed