D: Fix ICE in gimplify_var_or_parm_decl.

An internal compiler error (ICE) was triggered in the D frontend during the gimplification of variable or parameter declarations, specifically related to assert statements. The assert’s result type was not consistently matching its expression type. This patch ensures type consistency and introduces a new build_trap_call function to streamline code generation for built-in trap calls, used in various parts of the D frontend.