Normalize backend's elf structures with system headers.
Forward to system headers when available.
fix Issue 13476 - Writing stubs for dynamically loaded functions no longer works. (circular reference)
need explicit function call for c_long_double
fix Issue 13479 - Templates not emitted when instantiated in mixins mixed in functions

In the PR #3948, I changed the position where `TemplateInstance`s are inserted.

https://github.com/D-Programming-Language/dmd/pull/3948/files#diff-0477a1d81a6a920c99362954179c59c8R5937

But, I didn't notice that glue-layer does not handle `TemplateInstance`s in local members.
Add test case for issue 13478.

The issue was a 2.066 regression that has been fixed differently
on master in the meantime. This adds the test case from the
2.066 branch commit 972c90f.
Merge pull request #3991 from 9rnsr/fix13479

[REG2.067a] Issue 13479 - Templates not emitted when instantiated in mixins mixed in functions
Merge pull request #3996 from klickverbot/issue-13478-tests

Add test case for issue 13478.
Merge pull request #3990 from WalterBright/fix-long-double

need explicit function call for c_long_double
Merge pull request #3989 from 9rnsr/fix13476

[REG2.065] Issue 13476 - Writing stubs for dynamically loaded functions no longer works. (circular reference)
add C++ mangling c_long and c_ulong
resolve warning in typinf.c
Merge pull request #3999 from WalterBright/typinf-warning

resolve warning in typinf.c
fix Issue 13484 - Template type deduction from delegate parameter fails

The implicit conversion of expressions to delegates was added in 0.165 (a2b1fa4978948ca4d293c38666bd607c03ba791a, http://www.digitalmars.com/d/1.0/changelog2.html#new0165), but it was replaced with lazy parameter.
fix Issue 13481 - bug with inferring attributes from built-in properties
fix Issue 13472 - trying to insert a null into an array of object segfaults the compiler
Merge pull request #3994 from 9rnsr/fix13472

[REG2.066] Issue 13472 - trying to insert a null into an array of object segfaults the compiler
fix Issue 13490 - Can't append to array of structs with alias this as lvalue ternary opoerator result
Merge pull request #4001 from 9rnsr/fix13481

Issue 13481 - bug with inferring attributes from built-in properties
Merge pull request #3997 from WalterBright/c_long

add C++ mangling c_long and c_ulong
Merge pull request #4000 from 9rnsr/fix13484

Issue 13484 - Template type deduction from delegate parameter fails