linux-musl: Add patch to fix build error on hexagon

rust-lang/rust#121666 caused regression on hexagon linux-musl:

```
 ld.lld: error: undefined symbol: pthread_getname_np
```

Author: taiki-e

docker/test-base/patches/std+hexagon-unknown-linux-musl.diff

@@ -0,0 +1,24 @@
+diff --git a/src/sys/pal/unix/thread.rs b/src/sys/pal/unix/thread.rs
+index 2af6382..acf3ecb 100644
+--- a/src/sys/pal/unix/thread.rs
++++ b/src/sys/pal/unix/thread.rs
+@@ -225,7 +225,9 @@ pub fn set_name(_name: &CStr) {
+         // Newlib, Emscripten, and VxWorks have no way to set a thread name.
+     }
+ 
+-    #[cfg(target_os = "linux")]
++    // Qualcomm fork of musl doesn't have pthread_getname_np.
++    // https://github.com/quic/musl/blob/7243e0d3a9d7e0f08d21fc194a05749e0bb26725/include/pthread.h
++    #[cfg(all(target_os = "linux", not(target_arch = "hexagon")))]
+     pub fn get_name() -> Option<CString> {
+         const TASK_COMM_LEN: usize = 16;
+         let mut name = vec![0u8; TASK_COMM_LEN];
+@@ -253,7 +255,7 @@ pub fn get_name() -> Option<CString> {
+     }
+ 
+     #[cfg(not(any(
+-        target_os = "linux",
++        all(target_os = "linux", not(target_arch = "hexagon")),
+         target_os = "macos",
+         target_os = "ios",
+         target_os = "tvos",