fix Issue 13827 - Internal Compiler Error: null field
fix Issue 13831 - DMD crash on newing struct with overlapped fields in CTFE
fix Issue 13841 - infinite loop in compiler on simd arithmetic
Issue 13795 - Add longdouble to UnionExp to provide alignment
Merge pull request #4207 from Poita/Issue13795

Issue 13795 - Add longdouble to UnionExp to provide alignment
Merge pull request #4206 from 9rnsr/fix13841

Issue 13841 - infinite loop in compiler on simd arithmetic
Merge pull request #4204 from 9rnsr/fix13827

[REG2.067a] Issue 13827 - Internal Compiler Error: null field
Merge pull request #4205 from 9rnsr/fix13831

Issue 13831 - DMD crash on newing struct with overlapped fields in CTFE
fix Issue 13847 - CTFE internal error: dottype

Handle function values in each CTFE steps, then simplify
CallExp::interpret() and we need to interpret CallExp::e1 just only once.

After all, DotTypeExp will be one of the function values in CTFE, and
CallExp::interpret can distinguish 'virtual call' and 'direct call' properly.

Also simplify ThisExp::interpret because pthis is always interpreted to a
literal expression (TOKstructliteral or TOKclassreference).
fix Issue 13028 - [ICE] CTFE internal error: cannot evaluate at compile time
fix Issue 13528 - Internal Compiler Error: CTFE DotType
Explicitly truncate/widen shift value in OptimizeVisitor::PowExp
Merge pull request #4212 from ibuclaw/shiftcast

Explicitly truncate/widen shift value in OptimizeVisitor::PowExp
improve lexer error message
Merge pull request #4213 from WalterBright/lexermsg

improve lexer error message
Merge pull request #4208 from 9rnsr/fix13847

Issue 13847 - CTFE internal error: dottype
fix Issue 13832 - delegates that return ref do not output correctly to .di file