checkkconfigsymbols.sh: reimplementation in python

checkkconfigsymbols.sh: reimplementation in python

The scripts/checkkconfigsymbols.sh script searches Kconfig features
in the source code that are not defined in Kconfig. Such identifiers
always evaluate to false and are the source of various kinds of bugs.
However, the shell script is slow and it does not detect such broken
references in Kbuild and Kconfig files (e.g., ``depends on UNDEFINED´´).
Furthermore, it generates false positives. The script is also hard to
read and understand, and is thereby difficult to maintain.

This patch replaces the shell script with an implementation in Python,
which:
    (a) detects the same bugs, but does not report previous false positives
    (b) additionally detects broken references in Kconfig and all
        non-Kconfig files, such as Kbuild, .[cSh], .txt, .sh, defconfig, etc.
    (c) is up to 75 times faster than the shell script
    (d) only checks files under version control

The new script reduces the runtime on my machine (i7-2620M, 8GB RAM, SSD)
from 3m47s to 0m3s, and reports 938 broken references in Linux v3.17-rc1;
419 additional reports of which 16 are located in Kconfig files,
287 in defconfigs, 63 in ./Documentation, 1 in Kbuild.

Moreover, we intentionally include references in comments, which have been
ignored until now. Such comments may be leftovers of features that have
been removed or renamed in Kconfig (e.g., ``#endif /* CONFIG_MPC52xx */´´).
These references can be misleading and should be removed or replaced.

Note that the output format changed from (file list <tab> feature) to
(feature <tab> file list) as it simplifies the detection of the Kconfig
feature for long file lists.

Signed-off-by: Valentin Rothberg <valentinrothberg@gmail.com>
Signed-off-by: Stefan Hengelein <stefan.hengelein@fau.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>