Use libiberty's lrealpath to avoid portability problems.

Use libiberty's lrealpath to avoid portability problems.

The dmd front-end function FileName::canonicalName could be called
during the semantic pass of import("file") expressions, so still
requires that realpath() be redefined.

Initial patch by Rainer Orth.

gcc/d/ChangeLog:

2019-03-12  Iain Buclaw  <ibuclaw@gdcproject.org>

	PR d/87866
	* d-system.h (realpath): Redefine as lrealpath.

From-SVN: r269619