This is a release branch version of
r11-1741-g:31427b974ed7b7dd54e28fec595e731bf6eea8ba and
r11-2022-g:efe99cca78215e339ba79f0a900a896b4c0a3d36.

The trunk versions of the patch made GNU and Advanced SIMD vectors
distinct (but inter-convertible) in all cases.  However, the
traditional behaviour is that the types are distinct in template
arguments but not otherwise.

Following a suggestion from Jason, this patch puts the check
for different vector types under comparing_specializations.
In order to keep the backport as simple as possible, the patch
hard-codes the name of the attribute in the frontend rather than
adding a new branch-only target hook.

I didn't find a test that tripped the assert on the branch,
even with the --param in the PR, so instead I tested this by
forcing the hash function to only hash the tree code.  That made
the static assertion in the test fail without the patch but pass
with it.

This means that the tests pass for unmodified sources even
without the patch (unless you're very unlucky).

gcc/
	PR target/95726
	* config/aarch64/aarch64.c (aarch64_attribute_table): Add
	"Advanced SIMD type".
	* config/aarch64/aarch64-builtins.c: Include stringpool.h and
	attribs.h.
	(aarch64_init_simd_builtin_types): Add an "Advanced SIMD type"
	attribute to each Advanced SIMD type.
	* config/arm/arm.c (arm_attribute_table): Add "Advanced SIMD type".
	* config/arm/arm-builtins.c: Include stringpool.h and attribs.h.
	(arm_init_simd_builtin_types): Add an "Advanced SIMD type"
	attribute to each Advanced SIMD type.

gcc/cp/
	PR target/95726
	* typeck.c (structural_comptypes): When comparing template
	specializations, differentiate between vectors that have and
	do not have an "Advanced SIMD type" attribute.

gcc/testsuite/
	PR target/95726
	* g++.target/aarch64/pr95726.C: New test.
	* g++.target/arm/pr95726.C: Likewise.