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=7b2e4ccce29495a2f1c5bd13b0566fa7e0ef0cf0'>refs</a><a class='active' href='/guix/log/gnu/services/nix.scm'>log</a><a href='/guix/tree/gnu/services/nix.scm?id=7b2e4ccce29495a2f1c5bd13b0566fa7e0ef0cf0'>tree</a><a href='/guix/commit/gnu/services/nix.scm?id=7b2e4ccce29495a2f1c5bd13b0566fa7e0ef0cf0'>commit</a><a href='/guix/diff/gnu/services/nix.scm?id=7b2e4ccce29495a2f1c5bd13b0566fa7e0ef0cf0'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/services/nix.scm'>
<input type='hidden' name='id' value='7b2e4ccce29495a2f1c5bd13b0566fa7e0ef0cf0'/><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=7b2e4ccce29495a2f1c5bd13b0566fa7e0ef0cf0'>root</a>/<a href='/guix/log/gnu?id=7b2e4ccce29495a2f1c5bd13b0566fa7e0ef0cf0'>gnu</a>/<a href='/guix/log/gnu/services?id=7b2e4ccce29495a2f1c5bd13b0566fa7e0ef0cf0'>services</a>/<a href='/guix/log/gnu/services/nix.scm?id=7b2e4ccce29495a2f1c5bd13b0566fa7e0ef0cf0'>nix.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/gnu/services/nix.scm?id=7b2e4ccce29495a2f1c5bd13b0566fa7e0ef0cf0&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-12-06 17:48:48 +0800'>2020-12-06</span></td><td><a href='/guix/commit/gnu/services/nix.scm?id=8e73bf754f95fac5a383b90405e741d1cf1aaeb9'>services: nix: Move nix.conf generation to etc-service-type.</a><span class='msg-avail'>...</span></td><td>Zhu Zihao</td></tr>
<tr><td><span title='2020-07-25 12:27:35 +0300'>2020-07-25</span></td><td><a href='/guix/commit/gnu/services/nix.scm?id=64c6282e7fc69ff58e7257a7e72284f63f2f5956'>services: nix: Add extra-options.</a><span class='msg-avail'>...</span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2020-07-25 12:27:35 +0300'>2020-07-25</span></td><td><a href='/guix/commit/gnu/services/nix.scm?id=3601d802d55106e36e3279680d4728dd3cfe3b4c'>services: nix: Fix typo.</a><span class='msg-avail'>...</span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2020-07-25 12:27:35 +0300'>2020-07-25</span></td><td><a href='/guix/commit/gnu/services/nix.scm?id=ee67d193b3d1ddd18b10e845d5a75fbbf904b9c2'>services: nix: Export nix-configuration.</a><span class='msg-avail'>...</span></td><td>Peng Mei Yu</td></tr>
<tr><td><span title='2020-07-25 12:27:35 +0300'>2020-07-25</span></td><td><a href='/guix/commit/gnu/services/nix.scm?id=db65d7447c3adc46e2b24abfc07ae10c6c537df4'>services: nix: Provide nix commands.</a><span class='msg-avail'>...</span></td><td>Peng Mei Yu via Guix-patches via</td></tr>
<tr><td><span title='2020-07-22 22:10:11 +0300'>2020-07-22</span></td><td><a href='/guix/commit/gnu/services/nix.scm?id=4656180d5de1fef2846bea9af27ae509f32376ba'>services: nix: Fix sandbox.</a><span class='msg-avail'>...</span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2020-06-25 01:20:31 +0200'>2020-06-25</span></td><td><a href='/guix/commit/gnu/services/nix.scm?id=db170ee9210431cdbb3716a6b9a26ca5b6d931ee'>services: Add missing (ice-9 format) import.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>