intel/brw: allocate large table in the heap instead of the stack

When having a large number of virtual register this table can be too
large to be allocated on the stack.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30008>

src/intel/compiler/brw_fs_opt_virtual_grfs.cpp

@@ -34,7 +34,7 @@ brw_fs_opt_split_virtual_grfs(fs_visitor &s)
 
    /* Count the total number of registers */
    unsigned reg_count = 0;
-   unsigned vgrf_to_reg[num_vars];
+   unsigned *vgrf_to_reg = new unsigned[num_vars];
    for (unsigned i = 0; i < num_vars; i++) {
       vgrf_to_reg[i] = reg_count;
       reg_count += s.alloc.sizes[i];
@@ -203,6 +203,7 @@ cleanup:
    delete[] vgrf_has_split;
    delete[] new_virtual_grf;
    delete[] new_reg_offset;
+   delete[] vgrf_to_reg;
 
    return progress;
 }