Add print 'file'::var testcase with two libs defining the same global variable

gdb/testsuite/ChangeLog:

	* gdb.base/print-file-var-lib1.c, gdb.base/print-file-var-lib2.c,
	gdb.base/print-file-var-main.c, gdb.base/print-file-var.exp:
	New files.

gdb/ChangeLog:

        * config/djgpp/fnchange.lst: Add entries for print-file-var-lib1.c,
        print-file-var-lib2.c, print-file-var-main.c and
        print-file-var.exp (located in gdb/testsuite/gdb.base).