c.f.: https://raw.githubusercontent.com/nmeum/android-tools/237abccb95cadd78f2c431bc34974c2598804c21/patches/core/0022-Use-glibc-s-gettid-when-using-glibc-2.30.patch

diff -urpN a/core/libcutils/include/cutils/threads.h b/core/libcutils/include/cutils/threads.h
--- a/core/libcutils/include/cutils/threads.h	2018-06-20 17:58:42.000000000 -0700
+++ b/core/libcutils/include/cutils/threads.h	2019-11-12 07:26:44.612266274 -0800
@@ -37,7 +37,9 @@ extern "C" {
 /***********************************************************************/
 /***********************************************************************/
 
+#if !defined(__GLIBC__) || __GLIBC__ < 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ < 30)
 extern pid_t gettid();
+#endif
 
 #if !defined(_WIN32)
 
diff -urpN a/core/libcutils/threads.cpp b/core/libcutils/threads.cpp
--- a/core/libcutils/threads.cpp	2018-06-20 17:58:42.000000000 -0700
+++ b/core/libcutils/threads.cpp	2019-11-12 07:26:44.612266274 -0800
@@ -32,7 +32,7 @@
 #endif
 
 // No definition needed for Android because we'll just pick up bionic's copy.
-#ifndef __ANDROID__
+#if !defined(__ANDROID__) || !defined(__GLIBC__) || __GLIBC__ < 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ < 30)
 pid_t gettid() {
 #if defined(__APPLE__)
   uint64_t tid;