Make check_linker_need_libatomic more robust

setup.py

@@ -171,7 +171,17 @@ def check_linker_need_libatomic():
                                stdout=PIPE,
                                stderr=PIPE)
     cc_test.communicate(input=code_test)
-    return cc_test.returncode != 0
+    if cc_test.returncode == 0:
+        return False
+    # Double-check to see if -latomic actually can solve the problem.
+    # https://github.com/grpc/grpc/issues/22491
+    cc_test = subprocess.Popen(
+        ['cc', '-x', 'c++', '-std=c++11', '-latomic', '-'],
+        stdin=PIPE,
+        stdout=PIPE,
+        stderr=PIPE)
+    cc_test.communicate(input=code_test)
+    return cc_test.returncode == 0
 
 
 # There are some situations (like on Windows) where CC, CFLAGS, and LDFLAGS are