Make module files reproducible

Using lbasename ensures that the build path does not end up in the
module file.

Regtested on x86_64-pc-linux-gnu, committed to trunk. Will shortly
backport to the 6 and 7 branches as well.

2018-02-13  Alastair McKinstry  <alastair.mckinstry@sceal.ie>
	    Janne Blomqvist  <jb@gcc.gnu.org>

	* module.c (dump_module): Use lbasename to ensure that module
	files are reproducible.

Co-Authored-By: Janne Blomqvist <jb@gcc.gnu.org>

From-SVN: r257613

gcc/fortran/ChangeLog

+2018-02-13  Alastair McKinstry  <alastair.mckinstry@sceal.ie>
+	    Janne Blomqvist  <jb@gcc.gnu.org>
+
+	* module.c (dump_module): Use lbasename to ensure that module
+	files are reproducible.
+
 2018-02-12  Janus Weil  <janus@gcc.gnu.org>
 
 	PR fortran/84273

gcc/fortran/module.c

@@ -6148,8 +6148,10 @@ dump_module (const char *name, int dump_flag)
     gfc_fatal_error ("Can't open module file %qs for writing at %C: %s",
 		     filename_tmp, xstrerror (errno));
 
+  /* Use lbasename to ensure module files are reproducible regardless
+     of the build path (see the reproducible builds project).  */
   gzprintf (module_fp, "GFORTRAN module version '%s' created from %s\n",
-	    MOD_VERSION, gfc_source_file);
+	    MOD_VERSION, lbasename (gfc_source_file));
 
   /* Write the module itself.  */
   iomode = IO_OUTPUT;