Nest all namespaces

The compiler supports this now.  We can type less going forward.
No functional changes.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I29d6fa4f9aacc0e381f1a7637294db0392466995
diff --git a/aos/libc/aos_strsignal_test.cc b/aos/libc/aos_strsignal_test.cc
index d854aab..7e91d46 100644
--- a/aos/libc/aos_strsignal_test.cc
+++ b/aos/libc/aos_strsignal_test.cc
@@ -5,9 +5,7 @@
 
 #include "gtest/gtest.h"
 
-namespace aos {
-namespace libc {
-namespace testing {
+namespace aos::libc::testing {
 
 // Tries a couple of easy ones.
 TEST(StrsignalTest, Basic) {
@@ -45,6 +43,4 @@
 }
 #endif
 
-}  // namespace testing
-}  // namespace libc
-}  // namespace aos
+}  // namespace aos::libc::testing