KMI Whitelists: Add functionality to make whitelists additive

KMI Whitelists: Add functionality to make whitelists additive

If multiple KMI whitelists are specified, either by passing
--kmi-whitelist several times or by having multiple whitelist sections
in the whitelist files, the generated suppressions are created as an
intersection of symbols. That is rather unusual, as whitelisting should
rather work additive. That means that the symbols (or expressions
thereof) defined across several sections or files shall be considered a
union of symbols. This patch combines the whitelist parsing to create
exactly one function_suppression and one variable suppression. A test
case has been added to ensure the functionality is working.

Please note, migrating the existing code to this new functionality is
done in a separate commit.

	* include/abg-tools-utils.h
	(gen_suppr_spec_from_kernel_abi_whitelists): New function.
	* src/abg-tools-utils.cc
	(gen_suppr_spec_from_kernel_abi_whitelists): Likewise.
	* tests/.gitignore: Ignore new test executable.
	* tests/Makefile.am: Add new test executable.
	* tests/data/test-kmi-whitelist/whitelist-with-another-single-entry:
	New test input file.
	* tests/data/test-kmi-whitelist/whitelist-with-duplicate-entry:
	Likewise.
	* tests/data/test-kmi-whitelist/whitelist-with-single-entry:
	Likewise.
	* tests/data/test-kmi-whitelist/whitelist-with-two-sections:
	Likewise.
	* tests/data/Makefile.am: Add above test material.
	* tests/test-kmi-whitelist.cc: Add new test executable.

Reviewed-by: Dodji Seketeli <dodji@seketeli.org>
Signed-off-by: Matthias Maennich <maennich@google.com>