gcn/mkoffload.cc: Pass -save-temps on for the hsaco step

For the assembly/linking step of the device code, the "-save-temps" was not
passed on, such that amdgcn-amdhsa/bin/as and amdgcn-amdhsa's collect2
were invoked with '-o /tmp/cc...' and '@/tmp/cc...', respectively.
The -dump... prefix (...mkoffload.hsaco) was already properly set.

gcc/ChangeLog:

	* config/gcn/mkoffload.cc (main): Pass -save-temps on for the
	hsaco assemble/link.
	

diff --git a/gcc/config/gcn/mkoffload.cc b/gcc/config/gcn/mkoffload.cc
index 9493f89fec3..61bc9273077 100644
--- a/gcc/config/gcn/mkoffload.cc
+++ b/gcc/config/gcn/mkoffload.cc
@@ -1082,6 +1082,9 @@ main (int argc, char **argv)
       if (verbose)
 	obstack_ptr_grow (&ld_argv_obstack, "-v");
 
+      if (save_temps)
+	obstack_ptr_grow (&ld_argv_obstack, "-save-temps");
+
       for (int i = 1; i < argc; i++)
 	if (startswith (argv[i], "-l")
 	    || startswith (argv[i], "-Wl")