TLS-related functions (`__aeabi_read_tp`, `__tls_get_addr`) are not introduced
to bionic libc until Android 10. `__builtin_thread_pointer` will omit calls to
`__aeabi_read_tp` on arm, and causes build failure when `__ANDROID_API__` < 29.

TLS slot 1 has been used to storage thread id since Android 1.6 [1], and hasn't
changed until Android 14 [2,3]. If `__builtin_thread_pointer` is not available,
the default code path uses the method mentioned above to obtain a unique thread
id, and there doesn't seem to be anything wrong with this. If necessary in the
future, other methods can be made up for it, such as calling `pthread_self`. 

Besides, force using Emulated TLS for better compatibility.

[1]: https://android.googlesource.com/platform/bionic/+/refs/tags/android-1.6_r1/libc/private/bionic_tls.h#57
[2]: https://android.googlesource.com/platform/bionic/+/refs/heads/android14-dev/libc/platform/bionic/tls_defines.h#86
[3]: https://android.googlesource.com/platform/bionic/+/refs/heads/android14-dev/libc/platform/bionic/tls_defines.h#106

The error message is as follows.

```
  = note: ld.lld: error: undefined symbol: __aeabi_read_tp
          >>> referenced by static.c
          >>>               98cfcaec7182b1d8-static.o:(mi_free) in archive /tmp/rustcp5Rvgx/liblibmimalloc_sys-7086a69efa004ab8.rlib
          >>> referenced by static.c
          >>>               98cfcaec7182b1d8-static.o:(_mi_arena_segment_clear_abandoned) in archive /tmp/rustcp5Rvgx/liblibmimalloc_sys-7086a69efa004ab8.rlib
          >>> referenced by static.c
          >>>               98cfcaec7182b1d8-static.o:(_mi_arena_segment_clear_abandoned) in archive /tmp/rustcp5Rvgx/liblibmimalloc_sys-7086a69efa004ab8.rlib
          >>> referenced 9 more times
          clang-17: error: linker command failed with exit code 1 (use -v to see invocation)
```

--- a/build.rs
+++ b/build.rs
@@ -24,7 +28,10 @@
 
     let dynamic_tls = env::var("CARGO_FEATURE_LOCAL_DYNAMIC_TLS").is_ok();
 
-    if target_family == "unix" && target_os != "haiku" {
+    if target_family == "unix" && target_os == "android" {
+        build.flag_if_supported("-femulated-tls");
+    }
+    else if target_family == "unix" && target_os != "haiku" {
         if dynamic_tls {
             build.flag_if_supported("-ftls-model=local-dynamic");
         } else {
--- a/c_src/mimalloc/include/mimalloc/prim.h
+++ b/c_src/mimalloc/include/mimalloc/prim.h
@@ -205,7 +205,7 @@
 
 // Do we have __builtin_thread_pointer? (do not make this a compound test as it fails on older gcc's, see issue #851)
 #if defined(__has_builtin)
-#if __has_builtin(__builtin_thread_pointer)
+#if __has_builtin(__builtin_thread_pointer) && (!defined(__ANDROID__) || __ANDROID_API__ >= 29)
 #define MI_HAS_BUILTIN_THREAD_POINTER  1
 #endif
 #elif defined(__GNUC__) && (__GNUC__ >= 7) && defined(__aarch64__)  // special case aarch64 for older gcc versions (issue #851)