asan: adjust module name for global variables

As mentioned in the PR, when we use LTO, we wrongly use ltrans output
file name as a module name of a global variable. That leads to a
non-reproducible output.

After the suggested change, we emit context name of normal global
variables. And for artificial variables (like .Lubsan_data3), we use
aux_base_name (e.g. "./a.ltrans0.ltrans").

	PR sanitizer/108834

gcc/ChangeLog:

	* asan.cc (asan_add_global): Use proper TU name for normal
	global variables (and aux_base_name for the artificial one).

gcc/testsuite/ChangeLog:

	* c-c++-common/asan/global-overflow-1.c: Test line and column
	info for a global variable.