Add prototype for a function we call.

Author: jasonmolenda

lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-caching/a.c

@@ -1,5 +1,7 @@
 typedef float float4;
 
+int a();
+
 int main() {
   float4 f = 4.0f;
   // break here