Fix gdb.ada bp_fun_addr failure due to conflict between fun 'a' and s-dimmks.ads...

Fix gdb.ada bp_fun_addr failure due to conflict between fun 'a' and s-dimmks.ads 'A'.

The test fails (timeout) due to:
  (gdb) PASS: gdb.ada/bp_fun_addr.exp: break *a'address
  run
  Starting program: /bd/home/philippe/gdb/git/build_info_t/gdb/testsuite/outputs/gdb.ada/bp_fun_addr/a
  Multiple matches for a
  [0] cancel
  [1] a at /bd/home/philippe/gdb/git/info_t/gdb/testsuite/gdb.ada/bp_fun_addr/a.adb:18
  [2] system.dim.mks.a at s-dimmks.ads:115
  > FAIL: gdb.ada/bp_fun_addr.exp: run until breakpoint at a'address (timeout)
  testcase /home/philippe/gdb/git/build_info_t/gdb/testsuite/../../../info_t/gdb/testsuite/gdb.ada/bp_fun_addr.exp completed in 10 seconds

Fix this by using a fun name that has more chances to be unique.

2018-12-24  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* gdb.ada/bp_fun_addr/a.adb (a): Rename to bp_fun_addr.
	Filename a.adb changed to bp_fun_addr.adb.
	gdb.ada/bp_fun_addr.exp: Update test accordingly.