kconfig: check for out-of-bounds numeric constants

The Kconfig interpreter internally represents constants as strings, then
attempts to parse them as 64-bit signed integers for 'int' options, and
64-bit unsigned integers for 'hex' options.

However, there is currently no check that the conversion succeeds, leading
to failures when the values are actually used. For example:

  config LARGE_INT
    int
    default 10000000000000000000

  config BUGGED_INT_COMPARISON
    bool
    default y if LARGE_INT < 2

Obviously 10000000000000000000 is larger than 2, but the Kconfig
interpreter will fallback to comparing the two values with strcmp() after
the numeric conversion fails, causing the first character, '1', to be
compared with '2', and giving the wrong result.

Since none of these out-of-bounds values are used as constants anywhere in
the tree, we can already 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/20260915211508.291790-3-julianbraha@gmail.com
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

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