Fixes rust-lang#68489

When checking two `TokenStreams` to see if they are 'probably equal',
we ignore the `IsJoint` information associated with each `TokenTree`.
However, the `IsJoint` information determines whether adjacent tokens
will be 'glued' (if possible) when construction the `TokenStream` - e.g.
`[Gt Gt]` can be 'glued' to `BinOp(Shr)`.

Since we are ignoring the `IsJoint` information, 'glued' and 'unglued'
tokens are equivalent for determining if two `TokenStreams` are
'probably equal'. Therefore, we need to 'unglue' all tokens in the
stream to avoid false negatives (which cause us to throw out the cached
tokens, losing span information).

Some tokens need to be broken in a loop until we reach
'unbreakable' tokens.

When MSVC's `link.exe` wasn't found but another `link.exe` was, the error message given can be impenetrable to many users. The usual suspect is GNU's `link` tool. In this case, inform the user that they may need to install VS build tools.

This only applies when Microsoft's link tool is expected. Not `lld-link` or other MSVC compatible linkers.

rustc-book: Document `-Z strip=val` option

cc rust-lang#72110

…h-search-behaviour, r=kinnison

Fix going back in history to a search result page on firefox

This bug was actually firefox not re-running JS script when you go back in history. To trigger it on the current docs:

 * Make a search
 * Pick an element (which isn't on the same page as the current element!)
 * Go back in history

Instead of having the search results, you'll see the normal doc page. You can find a small explanation about it [here](http://web.archive.org/web/20100428053932/http://www.firefoxanswer.com/firefox/672-firefoxanswer.html).

r? @kinnison

cc @ollie27

…ochenkov

Suggest installing VS Build Tools in more situations

When MSVC's `link.exe` wasn't found but another `link.exe` was, the error message given can be [impenetrable](https://pastebin.com/MRMCr7HM) to many users. The usual suspect is GNU's `link` tool. In this case, inform the user that they may need to install VS build tools.

This only applies when Microsoft's link tool is expected.

…petrochenkov

Break tokens before checking if they are 'probably equal'

Fixes rust-lang#68489
Fixes rust-lang#70987

When checking two `TokenStreams` to see if they are 'probably equal',
we ignore the `IsJoint` information associated with each `TokenTree`.
However, the `IsJoint` information determines whether adjacent tokens
will be 'glued' (if possible) when construction the `TokenStream` - e.g.
`[Gt Gt]` can be 'glued' to `BinOp(Shr)`.

Since we are ignoring the `IsJoint` information, 'glued' and 'unglued'
tokens are equivalent for determining if two `TokenStreams` are
'probably equal'. Therefore, we need to 'unglue' all tokens in the
stream to avoid false negatives (which cause us to throw out the cached
tokens, losing span information).

…r=ecstatic-morse

Remove unused `StableHashingContext::node_to_hir_id` method

cc rust-lang#50928

llvm: Expose tiny code model to users

This model is relevant to embedded AArch64 targets and was added to LLVM relatively recently (https://reviews.llvm.org/D49673, mid 2018), so rustc frontend didn't provide access to it with `-C code-model`. The gcc analogue is [`-mcmodel=tiny`](https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html).
(This is one of the options that are passed directly to LLVM without being interpreted by rustc.)

Follow up to rust-lang#72248.