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);
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<tr><td><span title='2019-08-14 21:29:53 +0200'>2019-08-14</span></td><td><a href='/guix/commit/gnu/packages/bootstrap.scm?id=67dac6b8920755cb011047157bb7b4fae4760143'>gnu: mingw: Add x86_64 support.</a><span class='msg-avail'>...</span></td><td>Carl Dong</td></tr>
<tr><td><span title='2019-07-15 10:01:05 +0200'>2019-07-15</span></td><td><a href='/guix/commit/gnu/packages/bootstrap.scm?id=266e54e2acebf7a5ba51422269a0af677c9934a4'>gnu: guile-bootstrap: Use the new 'derivation' calling convention.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-05-29 15:40:31 +0200'>2019-05-29</span></td><td><a href='/guix/commit/gnu/packages/bootstrap.scm?id=7180dd671697e0215b140ebc0d36047b4b8375f2'>gnu: Add basic support for riscv64-linux-gnu targets.</a><span class='msg-avail'>...</span></td><td>Carl Dong</td></tr>
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