Fix tests using only-i686 to use the correct only-x86 directive

We translate `i686` to `x86` which means tests marked as `only-i686`
never ran. Update those tests to use `only-x86`.

src/test/ui/extern/extern-methods.rs

@@ -1,5 +1,5 @@
 // run-pass
-// only-i686
+// only-x86
 
 trait A {
     extern "fastcall" fn test1(i: i32);

src/test/ui/extern/extern-thiscall.rs

@@ -1,5 +1,5 @@
 // run-pass
-// only-i686
+// only-x86
 
 #![feature(abi_thiscall)]
 

src/test/ui/extern/extern-vectorcall.rs

@@ -1,7 +1,7 @@
 // run-pass
 // revisions: x64 x32
 // [x64]only-x86_64
-// [x32]only-i686
+// [x32]only-x86
 
 #![feature(abi_vectorcall)]
 

src/tools/compiletest/src/header/tests.rs

@@ -168,7 +168,7 @@ fn only_target() {
     let mut config = config();
     config.target = "x86_64-pc-windows-gnu".to_owned();
 
-    assert!(check_ignore(&config, "// only-i686"));
+    assert!(check_ignore(&config, "// only-x86"));
     assert!(check_ignore(&config, "// only-linux"));
     assert!(check_ignore(&config, "// only-msvc"));
     assert!(check_ignore(&config, "// only-32bit"));