Use different syscall constants on Android

src/platform-linux.cc

Index: src/platform-linux.cc
===================================================================
--- src/platform-linux.cc	(revision 7276)
+++ src/platform-linux.cc	(working copy)
@@ -803,7 +803,11 @@
 
 static int GetThreadID() {
   // Glibc doesn't provide a wrapper for gettid(2).
+#if defined(ANDROID)
+  return syscall(__NR_gettid);
+#else
   return syscall(SYS_gettid);
+#endif
 }
 
 
@@ -967,7 +971,11 @@
   void SendProfilingSignal(int tid) {
     if (!signal_handler_installed_) return;
     // Glibc doesn't provide a wrapper for tgkill(2).
+#if defined(ANDROID)
+    syscall(__NR_tgkill, vm_tgid_, tid, SIGPROF);
+#else
     syscall(SYS_tgkill, vm_tgid_, tid, SIGPROF);
+#endif
   }
 
   void Sleep(SleepInterval full_or_half) {