coccinelle: exclude sha1dc source files from static analysis

coccinelle: exclude sha1dc source files from static analysis

sha1dc is an external library, that we carry in-tree for convenience
or grab as a submodule, so there is no use in applying our semantic
patches to its source files.

Therefore, exclude sha1dc's source files from Coccinelle's static
analysis.

This change also makes the static analysis somewhat faster: presumably
because of the heavy use of repetitive macro declarations, applying
the semantic patches 'array.cocci' and 'swap.cocci' to 'sha1dc/sha1.c'
takes over half a minute each on my machine, which amounts to about a
third of the runtime of applying these two semantic patches to the
whole git source tree.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>