Sort loop variables to make sure Travis CI runs are reproducable.

reference/shaders/frag/for-loop-init.frag

@@ -11,7 +11,7 @@ void main()
     {
         FragColor += 10;
     }
-    for (mediump int j = 4, i_1 = 1; i_1 < 30; i_1++, j += 4)
+    for (mediump int i_1 = 1, j = 4; i_1 < 30; i_1++, j += 4)
     {
         FragColor += 11;
     }

spirv_cross.cpp

@@ -3025,6 +3025,9 @@ void Compiler::analyze_variable_scope(SPIRFunction &entry)
 
 		// We have a loop variable.
 		header_block.loop_variables.push_back(loop_variable.first);
+		// Need to sort here as variables come from an unordered container, and pushing stuff in wrong order
+		// will break reproducability in regression runs.
+		sort(begin(header_block.loop_variables), end(header_block.loop_variables));
 		get<SPIRVariable>(loop_variable.first).loop_variable = true;
 	}
 }