Allow user to overwrite or not simulation environment context

This patch renders absolete the requirements of having the environment
variable ARC_MULTILIB_OPTIONS defined. Thus, when it is not defined,
the default procesor will be used. The default processor is given by
--with-cpu flag passed to the configure script when we build the
compiler. This is requiered when we want to run specific tests which are
checking for the default gcc driver parameters.

The simulator parameters can be addnotate from site.exp. Hence, we can ask
to have the simulation traces whenever we want.

2016-01-08  Claudiu Zissulescu  <[email protected]>

	* dejagnu/baseboards/arc-sim-nsimdrv.exp (ARC_MULTILIB_OPTIONS):
	Now is optional.
	(nsim_flags): Can be overwrite from site.exp.

Author: Claudiu Zissulescu

dejagnu/baseboards/arc-sim-nsimdrv.exp

@@ -30,7 +30,11 @@ load_generic_config "sim"
 load_base_board_description "basic-sim"
 
 # Any multilib options are set in an environment variable.
-process_multilib_options "$env(ARC_MULTILIB_OPTIONS)"
+if { [ info exists env(ARC_MULTILIB_OPTIONS) ] } {
+    process_multilib_options "$env(ARC_MULTILIB_OPTIONS)"
+} else {
+    process_multilib_options ""
+}
 
 # We need extra procedures to determine for which cpu we simulate.
 search_and_load_file "library file" "tool-extra.exp" ${boards_dir}
@@ -39,7 +43,9 @@ set xldflags "-Wl,--defsym=__DEFAULT_HEAP_SIZE=256m \
     -Wl,--defsym=__DEFAULT_STACK_SIZE=1024m"
 
 # Set common defaults
-set nsim_flags {}
+f ![info exists nsim_flags] {
+    set nsim_flags {}
+}
 lappend nsim_flags \
 	-on nsim_isa_spfp \
 	-on nsim_isa_dpfp \