threads.h: avoid defining gettid on glibc >= 2.32

Glibc >=2.32 exposes a gettid() which clashes with libcutils
thread.h, so add a check to not expose it if building against
newer glibc (ChromiumOS will still use glibc 2.27 besides 2.32).

Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=1182060
Test: Builds without errors on both glibc 2.32 and 2.27.

Change-Id: Ib71fa1bc9fa185e3668002407dbed05a80c87740

libcutils/include/cutils/threads.h

@@ -31,7 +31,9 @@ extern "C" {
 //
 // Deprecated: use android::base::GetThreadId instead, which doesn't truncate on Mac/Windows.
 //
+#if !defined(__GLIBC__) || __GLIBC__ >= 2 && __GLIBC_MINOR__ < 32
 extern pid_t gettid();
+#endif
 
 #ifdef __cplusplus
 }

libcutils/threads.cpp

@@ -25,8 +25,9 @@
 #include <windows.h>
 #endif
 
-#if defined(__BIONIC__)
+#if defined(__BIONIC__) || defined(__GLIBC__) && __GLIBC_MINOR__ >= 32
 // No definition needed for Android because we'll just pick up bionic's copy.
+// No definition needed for Glibc >= 2.32 because it exposes its own copy.
 #else
 pid_t gettid() {
 #if defined(__APPLE__)