[DebugInfo] Fix DIE value emitters to be compatible with DWARF64 (2/19).

DW_FORM_sec_offset and DW_FORM_strp imply values of different sizes with
DWARF32 and DWARF64. The patch fixes DIE value classes to use correct
sizes when emitting their values. For DIELocList it ensures that the
requested DWARF form matches the current DWARF format because that class
uses a method that selects the size automatically.

Differential Revision: https://reviews.llvm.org/D87009