[trivial] Remove tautological null check.
Issue 11503 - immutable return value from pure function implicitly converts to mutable.
Remove CallExp::implicitCastTo altogether.

The pure -> immutable case is checked in implicitConvTo as well,
and since it yields MATCHexact, the castTo() in
Expression::implicitCastTo is a no-op anyway.
Issue 11909 - Struct members and static arrays break pure function escape analysis (immutability violation).
Clarify traverseIndirections implementation.

No functional change intended.
Make traverseIndirections() return bool instead of int.
Merge pull request #3149 from klickverbot/trivial-null-check

[trivial] Remove tautological null check.
Merge pull request #3148 from 9rnsr/fix11982

Issue 11982 - ICE(func.c) With function literal with no body
Add test case for issue 11969
Merge pull request #3144 from yebblies/MOD

[DDMD] MODxxx is unsigned char, not unsigned
fix Issue 11993 - typeof(this) in constraint of member function template should reflect method qualifier
Merge pull request #3150 from 9rnsr/fix11969

Add test case for issue 11969
Merge pull request #3151 from 9rnsr/fix11993

[REG] Issue 11993 - typeof(this) in constraint of member function template should reflect method qualifier
C++ mangle. Additional cases and tests for unix.

class mangle, volatile et c.
disable array passing test

disable static array arguments mangling.
disable a ctor mangling
Merge pull request #3116 from IgorStepanov/cppmangleunix

C++ mangle. Additional cases and tests for unix.
Fix some new D incompatibilities
Disable rtti
Move TypeInfo::toDt into a visitor class