Remove __unittest_toString and associated version(druntime_unittest).

This was introduced as part of GitHub pull request #41, which
was questionable (!) support code for D-Programming-Language/dmd#263.
However, the latter never materialized and __unittest_toString plus
version(druntime_unittest) were just confusing oddities at this point.
Merge pull request #856 from klickverbot/remove-dead-tostring

Remove __unittest_toString and associated version(druntime_unittest).
[trivial] Make rt.minfo import in object_.d function-local.

The 2.065 frontend trips over this when building the druntime
tests in shared library mode with LDC (forward reference to the
Object base class of TypeInfo when accessing the latter from
within rt.util.container). No idea why this happens, or why it
doesn't with DMD, but this fixes it and it also is a small
improvement on its own regardless.
test/*/Makefile: Do not assume that $(ROOT) is a relative path.

This allows us (LDC) to use the Makefiles in out-of-source builds.
Merge pull request #858 from klickverbot/test-out-of-source

test/*/Makefile: Do not assume that $(ROOT) is a relative path.
Merge pull request #857 from klickverbot/minfo-import

[trivial] Make rt.minfo import in object_.d function-local.
Mark core.sys.windows.windows.GetLastError as trusted
Merge pull request #861 from tom-tan/trusted-sys-windows-windows-GetLastError

Mark core.sys.windows.windows.GetLastError as trusted
Fix 12977 - lf64 definitions aren't correct on Solaris
Fix 12978 - struct sigaction is too small on 32-bit Solaris
Fix 13037 - SIGRTMIN and SIGRTMAX aren't correctly defined on Solaris
Merge pull request #859 from jasonbking/lf64

Multiple Solaris fixes