Remove the quad_precision_float feature gate

The f128 type has very little support in the compiler and the feature is
basically unusable today. Supporting half-baked features in the compiler can be
detrimental to the long-term development of the compiler, and hence this feature
is being removed.
Optimize out exhortations about being careful.

Yes, it is important to be careful, but repeated emphasis about it is probably
not helpful — it starts to sound like you came for a tutorial but found a
finger-wagging lecture.

Even after I removed a few of these comments, there are still several left in
the text. That's probably fine! A couple of mentions of how this is dangerous
and you ought to be careful may be a good reminder to the reader.

After making the edits, I reflowed the paragraphs that I had touched, using
emacs's "M-x fill-paragraph", with fill-column equal to 70.
auto merge of #15160 : alexcrichton/rust/remove-f128, r=brson

The f128 type has very little support in the compiler and the feature is
basically unusable today. Supporting half-baked features in the compiler can be
detrimental to the long-term development of the compiler, and hence this feature
is being removed.
auto merge of #15165 : zookoatleastauthoritycom/rust/14148-Optimize-out-exhortations-about-being-careful-2, r=huonw

Yes, it is important to be careful, but repeated emphasis about it is probably
not helpful — it starts to sound like you came for a tutorial but found a
finger-wagging lecture.

Even after I removed a few of these comments, there are still several left in
the text. That's probably fine! A couple of mentions of how this is dangerous
and you ought to be careful may be a good reminder to the reader.

After making the edits, I reflowed the paragraphs that I had touched, using
emacs's "M-x fill-paragraph", with fill-column equal to 70.
librustc: Don't try to perform the magical
vector-reference-to-unsafe-pointer-to-element cast if the type to be
casted to is not fully specified.

This is a conservative change to fix the user-visible symptoms of the
issue. A more flexible treatment would delay cast checks to after
function typechecking.

This can break code that did:

    let x: *u8 = &([0, 0]) as *_;

Change this code to:

    let x: *u8 = &([0, 0]) as *u8;

Closes #14893.

[breaking-change]
auto merge of #15164 : pcwalton/rust/vector-cast-weirdness, r=alexcrichton

vector-reference-to-unsafe-pointer-to-element cast if the type to be
casted to is not fully specified.

This is a conservative change to fix the user-visible symptoms of the
issue. A more flexible treatment would delay cast checks to after
function typechecking.

This can break code that did:

    let x: *u8 = &([0, 0]) as *_;

Change this code to:

    let x: *u8 = &([0, 0]) as *u8;

Closes #14893.

[breaking-change]

r? @alexcrichton
Merge branch 'master' of github.com:mozilla/rust into ios
Installation was broken for iOS

It tried to copy libraries which didn’t exist at all