[PATCH] libstdc++: Fix SFINAE for __is_intrinsic_type on ARM

[Matthias Kretz]

OK for master and all branches? (this issue only surfaced because of the new 
test)

------------ 8< -----------------

On ARM NEON doesn't support double, so __is_intrinsic_type_v<double,
whatever> should say false (instead of being ill-formed).

Signed-off-by: Matthias Kretz <m.kretz@gsi.de>

libstdc++-v3/ChangeLog:

	PR libstdc++/109261
	* include/experimental/bits/simd.h (__intrinsic_type):
	Specialize __intrinsic_type<double, 8> and
	__intrinsic_type<double, 16> in any case, but provide the member
	type only with __aarch64__.
---
 libstdc++-v3/include/experimental/bits/simd.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)


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 Dr. Matthias Kretz                           https://mattkretz.github.io
 GSI Helmholtz Centre for Heavy Ion Research               https://gsi.de
 stdₓ::simd
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