Makefile: run coccicheck on more source files

Makefile: run coccicheck on more source files

Before, when running the "coccicheck" target, only the source files
which were being compiled would have been checked by Coccinelle.
However, just because we aren't compiling a source file doesn't mean we
have to exclude it from analysis. This will allow us to catch more
mistakes, in particular ones that affect Windows-only sources since
Coccinelle currently runs only on Linux.

Make the "coccicheck" target run on all C sources except for those that
are taken from some third-party source. We don't want to patch these
files since we want them to be as close to upstream as possible so that
it'll be easier to pull in upstream updates.

When running a build on Arch Linux with no additional flags provided,
after applying this patch, the following sources are now checked:

* block-sha1/sha1.c
* compat/access.c
* compat/basename.c
* compat/fileno.c
* compat/gmtime.c
* compat/hstrerror.c
* compat/memmem.c
* compat/mingw.c
* compat/mkdir.c
* compat/mkdtemp.c
* compat/mmap.c
* compat/msvc.c
* compat/pread.c
* compat/precompose_utf8.c
* compat/qsort.c
* compat/setenv.c
* compat/sha1-chunked.c
* compat/snprintf.c
* compat/stat.c
* compat/strcasestr.c
* compat/strdup.c
* compat/strtoimax.c
* compat/strtoumax.c
* compat/unsetenv.c
* compat/win32/dirent.c
* compat/win32/path-utils.c
* compat/win32/pthread.c
* compat/win32/syslog.c
* compat/win32/trace2_win32_process_info.c
* compat/win32mmap.c
* compat/winansi.c
* ppc/sha1.c

This also results in the following source now being excluded:

* compat/obstack.c

Instead of generating $(FOUND_C_SOURCES) from a
`$(shell $(FIND_SOURCE_FILES))` invocation, an alternative design was
considered which involved converting $(FIND_SOURCE_FILES) into
$(SOURCE_FILES) which would hold a list of filenames from the
$(FIND_SOURCE_FILES) invocation. We would simply filter `%.c` files into
$(ALL_C_SOURCES). $(SOURCE_FILES) would then be passed directly to the
etags, ctags and cscope commands. We can see from the following
invocation

	$ git ls-files '*.[hcS]' '*.sh' ':!*[tp][0-9][0-9][0-9][0-9]*' ':!contrib' | wc -c
	   12779

that the number of characters in this list would pose a problem on
platforms with short command-line length limits (such as CMD which has a
max of 8191 characters). As a result, we don't perform this change.

However, we can see that the same issue may apply when running
Coccinelle since $(COCCI_SOURCES) is also a list of filenames:

	if ! echo $(COCCI_SOURCES) | xargs $$limit \
		$(SPATCH) --sp-file $< $(SPATCH_FLAGS) \
		>$@+ 2>$@.log; \

This is justified since platforms that support Coccinelle generally have
reasonably long command-line length limits and so we are safe for the
foreseeable future.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>