Consistent qualifier ordering.

Change our handful of `constexpr static`s to the much more common
`static constexpr`. It's easier to "follow existing style" when there
aren't two existing styles to copy from, and all else being equal,
"majority wins" :-)

Test: treehugger
Change-Id: Ifbf0f62ab84c9450bf9c2e49e96915c126fd20c4
diff --git a/tests/system_properties_test.cpp b/tests/system_properties_test.cpp
index aa8fef4..b1dfe0b 100644
--- a/tests/system_properties_test.cpp
+++ b/tests/system_properties_test.cpp
@@ -498,7 +498,7 @@
     check_with_read_callback(name, value);
   }
 
-  constexpr static const char* kExtraLongLegacyError =
+  static constexpr const char* kExtraLongLegacyError =
       "Must use __system_property_read_callback() to read";
   for (const auto& property : long_properties) {
     const std::string& name = property.first;