Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/perf/jvmti/jvmti_agent.c b/tools/perf/jvmti/jvmti_agent.c
index f7eb63c..8810859 100644
--- a/tools/perf/jvmti/jvmti_agent.c
+++ b/tools/perf/jvmti/jvmti_agent.c
@@ -45,10 +45,12 @@
 static char jit_path[PATH_MAX];
 static void *marker_addr;
 
+#ifndef HAVE_GETTID
 static inline pid_t gettid(void)
 {
 	return (pid_t)syscall(__NR_gettid);
 }
+#endif
 
 static int get_e_machine(struct jitheader *hdr)
 {