Add rpath for the C runtime libraries

When linking against the C runtime, we usually add rpath entries for all
the paths. But the C++ runtime does not do this, which seems to break
linking on Ubuntu 17.10. So we now add rpath entries in the shared
object itself, which solves this problem (ticket:4605).

Belonging to [master]:
  - OpenModelica/OMCompiler#1967

SimulationRuntime/c/Makefile.in

@@ -24,7 +24,7 @@ FPMATHFORTRAN = @FPMATHFORTRAN@
 OMBUILDDIR = @OMBUILDDIR@
 
 ifeq ($(OMC_MINIMAL_RUNTIME),)
-LDFLAGS=-L$(OMBUILDDIR)/lib/@host_short@/omc @RT_LDFLAGS@ @RT_LDFLAGS_OPTIONAL@
+LDFLAGS=-L$(OMBUILDDIR)/lib/@host_short@/omc @RT_LDFLAGS@ @RT_LDFLAGS_OPTIONAL@ @RPATH@
 LDFLAGS_SIM=-L$(OMBUILDDIR)/lib/@host_short@/omc -L$(CDASKRDIR) @RT_LDFLAGS_SIM@ @RT_LDFLAGS_SIM_OPTIONAL@
 else
 LDFLAGS=-L$(OMBUILDDIR)/lib/@host_short@/omc @RT_LDFLAGS@