This introduces a new header that pulls in system includes for use only
in the DMD front-end part of the compiler, fixing up uses of problematic
functions that are prevalent throughout the code.

Commits merged from dmd.

    Fix build of the D frontend on the Hurd and KFreeBSD.
    Initial patch from Matthias Klose.
    https://github.com/dlang/dmd/pull/8893

    Don't care about D/C++ compatibility in C++ port.
    Fixes build error in https://gcc.gnu.org/PR87788
    https://github.com/dlang/dmd/pull/8895

    Allow compiling front-end headers with strict warnings.
    https://github.com/dlang/dmd/pull/8909

    Add root/system.h header for wrapping system includes.
    Fixes https://gcc.gnu.org/PR87865
    https://github.com/dlang/dmd/pull/8910

    Move checkedint to dmd/root.
    https://github.com/dlang/dmd/pull/8912

    Use rmem instead of libc for malloc() and strdup().
    https://github.com/dlang/dmd/pull/8913

    Use align(8) for alignment of UnionExp, fixing several BUS errors
    due to alignment issues on SPARC.
    https://github.com/dlang/dmd/pull/8914

    Don't pass NULL pointer as format parameter to errorSupplemental.
    https://github.com/dlang/dmd/pull/8916

gcc/d/ChangeLog:

2018-11-05  Iain Buclaw  <ibuclaw@gdcproject.org>

	PR d/87865
	* d-system.h: New file.

From-SVN: r265780