Fix gdb.ada/fun_renaming.exp by using more unique names.

Fix gdb.ada/fun_renaming.exp by using more unique names.

The test fails due to conflict between var 'next' and s-pooloc.adb next:
(gdb) print next(1)
Multiple matches for next
[0] cancel
[1] pack.next (integer) return integer at /bd/home/philippe/gdb/git/binutils-gdb/gdb/testsuite/gdb.ada/fun_renaming/pack.adb:19
[2] system.pool_local.next (system.address) return system.pool_local.acc_address at s-pooloc.adb:151
> FAIL: gdb.ada/fun_renaming.exp: print next(1) (timeout)

Fix by making the names and renamings more unique.

gdb/testsuite/ChangeLog
2018-12-26  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* gdb.ada/fun_renaming/pack.ads (Next): Rename to Fun_Rename_Test_Next.
	(Renamed_Next): Rename to Renamed_Fun_Rename_Test_Next.
	gdb.ada/fun_renaming/pack.adb (Next): Rename to Fun_Rename_Test_Next.
	gdb.ada/fun_renaming/fun_renaming.adb (N): Rename to Fun_Rename_Test_N.
	gdb.ada/fun_renaming.exp: Update accordingly.