Suppress harmless gcc missing initializers warnings in a test

Suppressing the warnings is ugly but less ugly than explicitly
specifying all the omitted elements in the array.

tests/sizers/boxsizer.cpp

@@ -130,6 +130,8 @@ void BoxSizerTestCase::Size1()
 
 void BoxSizerTestCase::Size3()
 {
+    wxGCC_WARNING_SUPPRESS(missing-field-initializers)
+
     // check that various combinations of minimal sizes and proportions work as
     // expected for different window sizes
     static const struct LayoutTestData
@@ -189,6 +191,8 @@ void BoxSizerTestCase::Size3()
         { { 1, 2, 3, }, { 100, 100, 100, },   0, {   0,   0,   0, }, true },
     };
 
+    wxGCC_WARNING_RESTORE(missing-field-initializers)
+
     wxWindow *child[3];
     child[0] = new wxWindow(m_win, wxID_ANY);
     child[1] = new wxWindow(m_win, wxID_ANY);