increase executable area size to 30MB

Big applications can exceed the 16MB limit we previously used.
Increasing this above 30MB (if/when desired) will require changes to
the ARM and PowerPC JIT code to work around immediate branch encoding
limits on those platforms,

src/compile.cpp

@@ -56,7 +56,7 @@ const unsigned MaxNativeCallFootprint = 4;
 
 const unsigned InitialZoneCapacityInBytes = 64 * 1024;
 
-const unsigned ExecutableAreaSizeInBytes = 16 * 1024 * 1024;
+const unsigned ExecutableAreaSizeInBytes = 30 * 1024 * 1024;
 
 enum Root {
   CallTable,