Fix problems with new compiler attribute checking in configure script.

The last changes to ast_gcc_attribute.m4 caused some problems checking for
various attributes, because the scope of the symbol the attribute is applied
to can be important; this patch allows the scope to be specified for the check.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@200985 65c4cc65-6c06-0410-ace0-fbb531ad65f3