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/stdatomic_test.cpp b/tests/stdatomic_test.cpp
index 7b98df2..727af87 100644
--- a/tests/stdatomic_test.cpp
+++ b/tests/stdatomic_test.cpp
@@ -181,7 +181,7 @@
 
 // And a rudimentary test of acquire-release memory ordering:
 
-constexpr static uint_least32_t BIG = 30'000'000ul; // Assumed even below.
+static constexpr uint_least32_t BIG = 30'000'000ul;  // Assumed even below.
 
 struct three_atomics {
   atomic_uint_least32_t x;