Prepare directory in case test_system fails

In gdb.base/fileio.c, some functions may depend on others.  For
example, test_rename renames a file to one directory which is created
in test_system.  That is means, if test_system fails, test_rename
fails too, which is not a good practise, IMO.

In test_system, system ("mkdir -p XX") is used to create directories
needed for test_rename.  In this patch, we use dejagnu remote_exec
proc to create these directories on host.

In my gdb testing, mingw32 host and arm-none-eabi target, system
("mkdir -p XX") doesn't work properly (this issue can be addressed
separately), and this patch fixes the following fails.

FAIL: gdb.base/fileio.exp: Renaming a directory to a non-empty directory returns ENOTEMPTY or EEXIST
FAIL: gdb.base/fileio.exp: Unlink a file
FAIL: gdb.base/fileio.exp: Unlinking a file in a directory w/o write access returns EACCES

gdb/testsuite:

2014-10-29  Yao Qi  <yao@codesourcery.com>

	* gdb.base/fileio.exp: Make directories on host.

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2014-10-29  Yao Qi  <yao@codesourcery.com>
+
+	* gdb.base/fileio.exp: Make directories on host.
+
 2014-10-29  Yao Qi  <yao@codesourcery.com>
 
 	* gdb.base/fileio.c (test_write): Close the file.

gdb/testsuite/gdb.base/fileio.exp

@@ -210,6 +210,13 @@ gdb_test continue \
 "Continuing\\..*system 4:.*OK$stop_msg" \
 "System with invalid command returns 127"
 
+# Prepare the directory for rename tests in case that test_system
+# failed to create.
+set dir1 [file join $outdir "dir1.fileio.test" "subdir.fileio.test"]
+remote_exec host "mkdir -p $dir1"
+set dir1 [file join $outdir "dir2.fileio.test"]
+remote_exec host "mkdir $dir1"
+
 gdb_test continue \
 "Continuing\\..*rename 1:.*OK$stop_msg" \
 "Rename a file"