Rename d-gcc-includes.h to d-system.h
[testsuite] Backport test42 changes

Backport changes which remove fragile asm
See https://github.com/D-Programming-Language/dmd/pull/1809
Backport fix for final methods in interfaces

from dmd-2.063, see https://github.com/D-
Programming-Language/dmd/pull/1781

This fixes the runnable/xtest46 test.
Optimise out dead catches, fix ICE with goto into a catch block.
Replace VolatileStatement with SynchronizedStatement.
Some more small IRState reductions.
Fix error when using stdin as input.
Add -femit-moduleinfo switch.
Move intrinsic handling out of IRState.
Refactor libcall/intrinsic handling.
Fix GCC GC-related bug where nested static functions cause collection whilst parent function body is still not finished.
Fix ICE in maybe_set_builtin_frontend.
Another GCC GC fix where lambdas/function literals cause collection under the same circumstances.  Turn on check-target-libphobos in build.
Use front end's FuncDeclaration::deferred to keep deferred nested
functions.
Merge fix from upstream.
Harden logic for marking pure as in 'has no side effects'
Merge fix from upstream pull.
std.digest unittest fixes.
Update gdc include dir in build files.
Remove special handling of class, reference and array types.