Allow const expressions in array sizes in OpenCL translation.

[robertszafa]

There is an error when translating the tests/ShallowWater2D_memory_reduction_fpga/module_dyn_shapiro_superkernel.f95 to OpenCL. $dim_size is undefined because eval() gets variable names instead of numbers. This change returns the array size as an expression in that case. Tested on sw2d and seems to be OK.

[wimvanderbauwhede]

Before I merge this, I'd like to see the code that causes the error. It is odd because there is full constant folding of expressions in variable declarations. So I want to understand why that expression did not get folded.

[robertszafa]

The code that causes the error is tests/ShallowWater2D_memory_reduction_fpga/module_dyn_shapiro_superkernel.f95. The code has not been memory reduced - it has parameters that are not folded.

I think there are two options: add folding to the translation pass (there is already a replace_param_by_val function), or use this change.