Documentation: x86: exception-tables: document CONFIG_BUILDTIME_TABLE_SORT

Documentation: x86: exception-tables: document CONFIG_BUILDTIME_TABLE_SORT

Provide more information about __ex_table sorting post link.

The exception tables and fixup tables use a commonly recurring pattern
in the kernel of storing the address of labels as date in custom ELF
sections, then finding these sections, iterating elements within them,
and possibly revisiting them or modifying the data at these addresses.

Sorting readonly arrays to minimize runtime penalties is quite clever.

Suggested-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20200327000951.84071-1-ndesaulniers@google.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>