Doctest coresimd::x86::__m256 failed on processors withouth "avx" feature.
Backported patch with changes from https://github.com/rust-lang-nursery/stdsimd/issues/481

--- rustc-1.26.2-src-orig/src/stdsimd/coresimd/x86/mod.rs	1970-01-01 05:00:00.000000000 +0500
+++ rustc-1.26.2-src/src/stdsimd/coresimd/x86/mod.rs	2018-06-22 00:01:55.142026720 +0500
@@ -293,13 +293,13 @@
     /// use std::arch::x86_64::*;
     ///
     /// # fn main() {
-    /// # #[target_feature(enable = "sse")]
+    /// # #[target_feature(enable = "avx")]
     /// # unsafe fn foo() {
     /// let eight_zeros = _mm256_setzero_ps();
     /// let eight_ones = _mm256_set1_ps(1.0);
     /// let eight_floats = _mm256_set_ps(1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0);
     /// # }
-    /// # if is_x86_feature_detected!("sse") { unsafe { foo() } }
+    /// # if is_x86_feature_detected!("avx") { unsafe { foo() } }
     /// # }
     /// ```
     pub struct __m256(f32, f32, f32, f32, f32, f32, f32, f32);
t'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=b9c410c089b535f283617f81bc193d8b4934bbc8'>refs</a><a class='active' href='/guix/log/tests/debug-link.scm'>log</a><a href='/guix/tree/tests/debug-link.scm?id=b9c410c089b535f283617f81bc193d8b4934bbc8'>tree</a><a href='/guix/commit/tests/debug-link.scm?id=b9c410c089b535f283617f81bc193d8b4934bbc8'>commit</a><a href='/guix/diff/tests/debug-link.scm?id=b9c410c089b535f283617f81bc193d8b4934bbc8'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/tests/debug-link.scm'>
<input type='hidden' name='id' value='b9c410c089b535f283617f81bc193d8b4934bbc8'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=b9c410c089b535f283617f81bc193d8b4934bbc8'>root</a>/<a href='/guix/log/tests?id=b9c410c089b535f283617f81bc193d8b4934bbc8'>tests</a>/<a href='/guix/log/tests/debug-link.scm?id=b9c410c089b535f283617f81bc193d8b4934bbc8'>debug-link.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/debug-link.scm?id=b9c410c089b535f283617f81bc193d8b4934bbc8&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2018-11-12 23:37:13 +0100'>2018-11-12</span></td><td><a href='/guix/commit/tests/debug-link.scm?id=9ed86fe175c15c819d6d86681c8136ff6bc927c0'>tests: Add 'test-assertm' to (guix tests).</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/tests.scm (test-assertm): New macro.
* tests/gexp.scm (test-assertm): Remove.
* tests/profiles.scm (test-assertm): Remove.
* tests/challenge.scm (%store, test-assertm): Remove.
* tests/debug-link.scm (%store, test-assertm): Remove.
* tests/size.scm (%store, test-assertm): Remove.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-08-24 18:01:05 +0200'>2018-08-24</span></td><td><a href='/guix/commit/tests/debug-link.scm?id=93c333895a4e2dc9baabec8ade60d9d2ac0a91e2'>grafts: Add (guix build debug-link) and use it.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/19973&gt;.
Reported by Mark H Weaver &lt;mhw@netris.org&gt;.

* guix/build/debug-link.scm: New file.
* guix/build/graft.scm (%graft-hooks): New variable.
(graft): Add #:hooks and honor it.
* guix/grafts.scm (graft-derivation/shallow): Add (guix build
debug-link) and (guix elf) to #:modules.
* tests/debug-link.scm: New file.
* Makefile.am (MODULES): Add guix/build/debug-link.scm.
(SCM_TESTS): Add tests/debug-link.scm.
</span></span></td><td>Ludovic Courtès</td></tr>