kconfig: check for hex and int mismatches

Using a numeric option of one type (e.g. 'int') to determine the value of
a different numeric type (e.g. 'hex') currently fails silently in various
ways if

kconfig: check for hex and int mismatches

Using a numeric option of one type (e.g. 'int') to determine the value of
a different numeric type (e.g. 'hex') currently fails silently in various
ways if attempted, because the underlying string representation is naively
reused.

Example 1:

config I
int
default -1

config HEX_DEFAULT_INT
hex
default I

Here, HEX_DEFAULT_INT actually gets set to '0x-1', which is of course not
a valid hex value.

Example 2:

config H
hex
default A

config INT_DEFAULT_HEX
int
default H

Here, INT_DEFAULT_HEX actually gets set to 'A', without even converting
into the base-10 equivalent of 10. This value, 'A', is otherwise a
rejected int value if entered in the frontend, or read in from an existing
.config file.

These int-hex mismatches currently do not appear anywhere in the tree, so
it is already safe to make these error out.

Assisted-by: LLM
Signed-off-by: Julian Braha <julianbraha@gmail.com>
Reviewed-by: Nicolas Schier <n.schier@fritz.com>
Link: https://patch.msgid.link/20260915211508.291790-4-julianbraha@gmail.com
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

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