Ignore some tests on platforms without libstd spans

Author: petrochenkov

src/test/ui/issues/issue-38857.rs

@@ -1,3 +1,8 @@
+// FIXME: missing sysroot spans (#53081)
+// ignore-i586-unknown-linux-gnu
+// ignore-i586-unknown-linux-musl
+// ignore-i686-unknown-linux-musl
+
 fn main() {
     let a = std::sys::imp::process::process_common::StdioPipes { ..panic!() };
     //~^ ERROR failed to resolve: could not find `imp` in `sys` [E0433]

src/test/ui/issues/issue-38857.stderr

@@ -1,11 +1,11 @@
 error[E0433]: failed to resolve: could not find `imp` in `sys`
-  --> $DIR/issue-38857.rs:2:23
+  --> $DIR/issue-38857.rs:7:23
    |
 LL |     let a = std::sys::imp::process::process_common::StdioPipes { ..panic!() };
    |                       ^^^ could not find `imp` in `sys`
 
 error[E0603]: module `sys` is private
-  --> $DIR/issue-38857.rs:2:18
+  --> $DIR/issue-38857.rs:7:18
    |
 LL |     let a = std::sys::imp::process::process_common::StdioPipes { ..panic!() };
    |                  ^^^ this module is private

src/test/ui/stability-in-private-module.rs

@@ -1,3 +1,8 @@
+// FIXME: missing sysroot spans (#53081)
+// ignore-i586-unknown-linux-gnu
+// ignore-i586-unknown-linux-musl
+// ignore-i686-unknown-linux-musl
+
 fn main() {
     let _ = std::thread::thread_info::current_thread();
     //~^ERROR module `thread_info` is private

src/test/ui/stability-in-private-module.stderr

@@ -1,5 +1,5 @@
 error[E0603]: module `thread_info` is private
-  --> $DIR/stability-in-private-module.rs:2:26
+  --> $DIR/stability-in-private-module.rs:7:26
    |
 LL |     let _ = std::thread::thread_info::current_thread();
    |                          ^^^^^^^^^^^ this module is private