Rollup merge of rust-lang#47514 - gnzlbg:whitelist_x86_fxsr, r=rkruppe

whitelist x86 fxsr feature

rust-lang#47223 properly checks that only white-listed features are allowed in combination with `target_feature`, but the `fxsr` feature used by `stdsimd` was not white-listed.

r? @alexcrichton

src/librustc_trans/llvm_util.rs

@@ -85,7 +85,8 @@ const X86_WHITELIST: &'static [&'static str] = &["avx\0", "avx2\0", "bmi\0", "bm
                                                  "avx512dq\0", "avx512er\0",
                                                  "avx512f\0", "avx512ifma\0",
                                                  "avx512pf\0", "avx512vbmi\0",
-                                                 "avx512vl\0", "avx512vpopcntdq\0", "mmx\0"];
+                                                 "avx512vl\0", "avx512vpopcntdq\0",
+                                                 "mmx\0", "fxsr\0"];
 
 const HEXAGON_WHITELIST: &'static [&'static str] = &["hvx\0", "hvx-double\0"];