[Analyzer] Correct stack address escape diagnostic

Summary:
Leaking a stack address via a static variable refers to it in the diagnostic as a 'global'. This patch corrects the diagnostic for static variables.


Patch by Phil Camp, SN Systems

Reviewers: dcoughlin, zaks.anna

Subscribers: xazax.hun, cfe-commits

Differential Revision: http://reviews.llvm.org/D19866

Patch by Phil Camp

llvm-svn: 270849