When compiling, this warning gives string literals the type const char[]
to help catch accidental modification (which is undefined behaviour).
There currently aren't any instances of this in flashrom, so let's
enable this warning to keep it that way. This requires adding const
qualifiers to the declarations of several variables that work with
string literals.

Change-Id: I62d9bc194938a0c9a0e4cdff7ced8ea2e14cc1bc
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/34577


Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>