fix Issue 12749 - Constructor-local function allows multiple mutation of immutable member
Improve diagnostic messages
require opEquals for AA keys

- Check that the compiler can generate a runtime function to test AA keys for equality.

- This is necessary to switch the druntime implementation from opCmp to opEquals.
Fix Issue 12824 - REG(2.066) ICE(statement.c) Segfault with label and static if
Merge pull request #3607 from yebblies/issue12824

Issue 12824 - REG(2.066) ICE(statement.c) Segfault with label and static if
Merge pull request #3599 from MartinNowak/opEqualsForAA

require opEquals for AA keys
Merge pull request #3555 from 9rnsr/fix12749

Issue 12749 - Constructor-local function allows multiple mutation of immutable member