Backports to 7.3

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

I've backported today following 23 patches after bootstrapping/regtesting
them on x86_64-linux and i686-linux.

Some of the backports are just partial backports, in particular for
r255133 I've just backported the removal of case BUILT_IN_STPNCPY_CHK:,
for r255354 the patch didn't apply at all, because we don't have the
C++ __builtin_unreachables with BUILTINS_LOCATION, so rewrote it manually,
and finally r255574 is just the fix, so am not trying to extend it to
reversed loops and of course it didn't apply cleanly either.

	Jakub

Attachment: r254952
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Attachment: r254990
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Attachment: r255004
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Attachment: r255051
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Attachment: r255095
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Attachment: r255115
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Attachment: r255117
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Attachment: r255133
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Attachment: r255134
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Attachment: r255144
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Attachment: r255150
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Attachment: r255167
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Attachment: r255180
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Attachment: r255226
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Attachment: r255353
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Attachment: r255354
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Attachment: r255456
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Attachment: r255486
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Attachment: r255574
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Attachment: r255623
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Attachment: r255626
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Attachment: r255697
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Attachment: r255702
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