Fix compiling on GCC9 am: 7e03757b7d am: c3ea2f3793

Change-Id: I7dcced6424a3c04698be2e7bac2dae51986324fc
diff --git a/src/core/lib/gpr/log_linux.cc b/src/core/lib/gpr/log_linux.cc
index 561276f..8b597b4 100644
--- a/src/core/lib/gpr/log_linux.cc
+++ b/src/core/lib/gpr/log_linux.cc
@@ -40,7 +40,7 @@
 #include <time.h>
 #include <unistd.h>
 
-static long gettid(void) { return syscall(__NR_gettid); }
+static long sys_gettid(void) { return syscall(__NR_gettid); }
 
 void gpr_log(const char* file, int line, gpr_log_severity severity,
              const char* format, ...) {
@@ -70,7 +70,7 @@
   gpr_timespec now = gpr_now(GPR_CLOCK_REALTIME);
   struct tm tm;
   static __thread long tid = 0;
-  if (tid == 0) tid = gettid();
+  if (tid == 0) tid = sys_gettid();
 
   timer = static_cast<time_t>(now.tv_sec);
   final_slash = strrchr(args->file, '/');
diff --git a/src/core/lib/gpr/log_posix.cc b/src/core/lib/gpr/log_posix.cc
index 0acb225..cd0b702 100644
--- a/src/core/lib/gpr/log_posix.cc
+++ b/src/core/lib/gpr/log_posix.cc
@@ -30,7 +30,7 @@
 #include <string.h>
 #include <time.h>
 
-static intptr_t gettid(void) { return (intptr_t)pthread_self(); }
+static intptr_t sys_gettid(void) { return (intptr_t)pthread_self(); }
 
 void gpr_log(const char* file, int line, gpr_log_severity severity,
              const char* format, ...) {
@@ -85,7 +85,7 @@
   char* prefix;
   gpr_asprintf(&prefix, "%s%s.%09d %7tu %s:%d]",
                gpr_log_severity_string(args->severity), time_buffer,
-               (int)(now.tv_nsec), gettid(), display_file, args->line);
+               (int)(now.tv_nsec), sys_gettid(), display_file, args->line);
 
   fprintf(stderr, "%-70s %s\n", prefix, args->message);
   gpr_free(prefix);
diff --git a/src/core/lib/iomgr/ev_epollex_linux.cc b/src/core/lib/iomgr/ev_epollex_linux.cc
index b082634..9a3e6dd 100644
--- a/src/core/lib/iomgr/ev_epollex_linux.cc
+++ b/src/core/lib/iomgr/ev_epollex_linux.cc
@@ -1146,7 +1146,7 @@
 }
 
 #ifndef NDEBUG
-static long gettid(void) { return syscall(__NR_gettid); }
+static long sys_gettid(void) { return syscall(__NR_gettid); }
 #endif
 
 /* pollset->mu lock must be held by the caller before calling this.
@@ -1166,7 +1166,7 @@
 #define WORKER_PTR (&worker)
 #endif
 #ifndef NDEBUG
-  WORKER_PTR->originator = gettid();
+  WORKER_PTR->originator = sys_gettid();
 #endif
   if (grpc_polling_trace.enabled()) {
     gpr_log(GPR_INFO,