Bug 24430 - Fold away const for array types

Bug 24430 - Fold away const for array types

In C and C++ the qualifiers of a qualified array type apply to the
element type of said array.

In this particular problem report, GCC and Clang emit DWARF that
represent the qualifiers either on the array type, or on the element
type.  Quoting the test of the bug:

    Given the following example:

	struct test {
	  const char asdf[4];
	};

	void func(struct test arg) {}

    abidiff says:

     1 function with some indirect sub-type change:

       [C]'function void func(test)' at test.c:5:1 has some indirect sub-type
     changes:
	 parameter 1 of type 'struct test' has sub-type changes:
	   type size hasn't changed
	   1 data member change:
	    type of 'const char test::asdf[4]' changed:
	      entity changed from 'const char[4]' to 'const char[4] const'

This is because GCC represents the array as const array of const
signed char, whereas clang represents it as an array of const signed
char.

In this patch, libabigail's DWARF reader detects qualified array types
and appropriately qualifies the array element type, instead of
qualifying the array type.  The patch accordingly adjusts the various
regression tests and adds a new test which comes from the problem
report.

	* include/abg-fwd.h (is_array_of_qualified_element): Declare 2
	overloads of this function.
	(re_canonicalize): Declare a new function.
	* include/abg-ir.h (class {decl_base, type_base}): Declare
	re_canonicalize as a friend of these classes.
	* src/abg-dwarf-reader.cc (maybe_strip_qualification): Detect
	qualified array types and appropriately qualifies the array
	element type, instead of qualifying the array type itself.
	Re-canonicalize the resulting type if necessary.
	* src/abg-ir.cc (is_array_of_qualified_element): Define 2
	overloads of this function.
	(re_canonicalize): Define new function.
	* tests/data/Makefile.am: The two new test binary input files
	PR24430-fold-qualified-array-clang and
	PR24430-fold-qualified-array-gcc to source distribution, as well
	as the expected reference output.
	* tests/data/test-annotate/test15-pr18892.so.abi: Adjust.
	* tests/data/test-annotate/test17-pr19027.so.abi: Likewise.
	* tests/data/test-annotate/test19-pr19023-libtcmalloc_and_profiler.so.abi:
	Likewise.
	* tests/data/test-annotate/test21-pr19092.so.abi: Likewise.
	* tests/data/test-diff-filter/PR24430-fold-qualified-array-clang:
	New binary test input coming from the bug report.
	* tests/data/test-diff-filter/PR24430-fold-qualified-array-gcc:
	Likewise.
	* tests/data/test-diff-filter/PR24430-fold-qualified-array-report-0.txt:
	Expected reference abi difference.
	* tests/data/test-diff-filter/test33-report-0.txt: Adjust.
	* tests/data/test-diff-pkg/nss-3.23.0-1.0.fc23.x86_64-report-0.txt:
	Likewise.
	* tests/data/test-read-dwarf/PR22122-libftdc.so.abi: Likewise.
	* tests/data/test-read-dwarf/test12-pr18844.so.abi: Likewise.
	* tests/data/test-read-dwarf/test15-pr18892.so.abi: Likewise.
	* tests/data/test-read-dwarf/test17-pr19027.so.abi: Likewise.
	* tests/data/test-read-dwarf/test19-pr19023-libtcmalloc_and_profiler.so.abi:
	Likewise.
	* tests/data/test-read-dwarf/test21-pr19092.so.abi: Likewise.
	* tests/data/test-read-dwarf/test22-pr19097-libstdc++.so.6.0.17.so.abi:
	Likewise.
	* tests/test-diff-filter.cc: Add the new binary test input to this
	test harness.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>