[libbacktrace] Fix btest-lto for older gcc

[libbacktrace] Fix btest-lto for older gcc

With gcc 4.8.5, btest_lto ends up with a privatized name for the variable with
name 'global':
...
$ nm btest_lto | grep ' d ' | grep global
0000000000617150 d global.2530
...
which makes test5 fail:
...
    test5: unexpected syminfo name got global.2530 expected global
...

Fix this failure by accepting this type of name as a valid name in btest_lto.

2019-02-26  Tom de Vries  <tdevries@suse.de>

	* btest.c (test5): Allow global.* as minimal symbol name for global.

From-SVN: r269217