Fix bogus zero-length array test.

Issue 7175 was about .ptr always giving null for a zero-length
static array in a struct, despite the fact that the struct has
size 1 and thus certainly a non-null address.

The test case as modified by 36c9b64, however, checks that a
free-standing zero-length static array on the stack has an
address, which is quite a different scenario. From the spec,
I don't see a reason why zero-sized objects should need any
memory associated with them, so I am reluctant to pessimize
LDC's codegen over this.
fix Issue 13403 - [ICE][2.067Alpha] Internal error: backend\type.c 332 with new package protection extension.
use checkedint to check overflow
Do not use octal literals in dmd
Add TemplateInstance::tnext to construct instantiation dependency graph

To detect speculative instantiations in codegen phase, `tnext` is neccesary for the `test6()` case `runnable/link13350.d`. That's a big difference from the PR #2550.
Get rid of Expression::toElem forwarding function
Merge pull request #3959 from yebblies/toElem

Get rid of Expression::toElem forwarding function
Fix Issue 13427 - [REG2.066] cannot inline default argument alloca(...)
Get rid of dt_t from the frontend
Remove all references to IRState from the frontend
Update gluestub
Merge pull request #3952 from yebblies/octal

[DDMD] Do not use octal literals in dmd
Merge pull request #3960 from yebblies/dt_t

Remove uses of dt_t and IRState from the frontend, and update gluestub.c
Fix deprecation messages in d_do_test
Merge pull request #3962 from yebblies/dtestenv

Fix deprecation messages in d_do_test
Use mem.malloc instead of new for aav.c
Merge pull request #3963 from yebblies/aavnew

[DDMD] Use mem.malloc instead of new for aav.c
Merge pull request #3961 from yebblies/issue13427

Issue 13427 - [REG2.066] cannot inline default argument alloca(...)
Fix Issue 8425 - Missing line number and module name that can't use core.simd
Merge pull request #2879 from yebblies/issue8425

Issue 8425 - Missing line number and module name that can't use core.simd