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 3918 - Parameter use before its use in an AndAnd expression with reals treats NaN as false
Normalize backend's elf structures with system headers.
Forward to system headers when available.
fix Issue 13403 - [ICE][2.067Alpha] Internal error: backend\type.c 332 with new package protection extension.
[Refactoring] fix indent in IsExp::semantic()
fix Issue 13350 - is(typeof(fun)) causes link error when template fun calls undefined reference

Evaluate the type in IsExp, then unspeculative declared symbols.
Merge pull request #3894 from 9rnsr/fix13350

Issue 13350 - is(typeof(fun)) causes link error when template fun calls undefined reference
Merge pull request #3812 from yebblies/issue3918

Issue 3918 - Parameter use before its use in an AndAnd expression with reals treats NaN as false
[Refactoring] TemplateInstance::semantic()

- Remove a goto jump
- Reduce code indent level
- Use ModToStc in TemplateThisParameter resolution
[Refactoring] Add Module::rootImports() and use it in TemplateInstance::needsCodegen()

it would make compilation a little faster so `rootImports` cache the result.
[Refactoring] Remove the hack code introduced in #1760

AST identity issue has been properly fixed in #3383 (fceb16bbf7).
use checkedint to check overflow
fix Issue 13417 - segmentation fault when deduce template type
Merge pull request #3945 from 9rnsr/refactor_template

[Refactoring] template.c
fix Issue 13424 - Initialization of delegate to do-nothing default causes segfault at runtime
Merge pull request #3950 from 9rnsr/fix13417

[REG2.066] Issue 13417 - segmentation fault when deduce template type
Merge pull request #3951 from 9rnsr/fix13424

[REG2.066] Issue 13424 - Initialization of delegate to do-nothing default causes segfault at runtime
Move error-related stuff into its own file and merge with color
Remove un-convertable comment
Do not use octal literals in dmd