fix Issue 9650 - __traits(compiles) + mixin

I couldn't minimize test case, but the bug fix is obvious.

The bug had been hiding for a long time, but recent Phobos change (https://github.com/D-Programming-Language/phobos/commit/2a88fea7867f33fd1cf15c2dca7790a3c8aea474) had exposed the bug.

When a mixin expression gets invalid code string, the parsing error had not handled correctly. In such case, it had generated *invalid* AST instead of returning ErrorExp. I guess that the invalid AST would report weird error in later semantic analysis.

I think that both CompileDeclaration and CompileStatement do not have same problem. So they are not changed.
Improve code gen for localgot
Cast T[] to integral type: deprecation -> error.
convert escape mask literal constant to ESCAPEmask
join declaration and first use for lots of variables
fix Issue 9726 - Add minimum % coverage required for -cov testing
Add assertion and fix AST identity that had broken by template instantiation
Fixes Issue 6089 - extern variable should not have an initializer.
Merge pull request #1758 from braddr/cleanup2

join declaration and first use for lots of variables
refactor libomf
refactor libomf
Merge pull request #1759 from WalterBright/fix9726

fix Issue 9726 - Add minimum % coverage required for -cov testing
Merge pull request #1752 from WalterBright/improvelocalgot

Improve code gen for localgot
Merge pull request #1762 from AndrejMitrovic/Fix6089

Issue 6089 - extern variable should not have an initializer.
Merge pull request #1757 from braddr/backend-escape

convert escape mask literal constant to ESCAPEmask
Merge pull request #1760 from 9rnsr/fix_ast_identity

Add assertion and fix AST identity that had broken by template instantiation
Fixes Issue 9727 - Unittest comment should appear before example.
Fixes Issue 9755 - Json template protection attribute output was wrong.
Merge pull request #1768 from AndrejMitrovic/Fix9755

Issue 9755 - Json template protection attribute output is wrong.
Merge pull request #1765 from AndrejMitrovic/Fix9727

Issue 9727 - Unittest comment should appear before example.