[GCOV] Add a test for function defined on one line (follow-up of https://reviews.llvm.org/D53600)

Summary: Add a test for coverage for function definition like void foo() { }.

Reviewers: marco-c

Reviewed By: marco-c

Subscribers: delcypher, llvm-commits, #sanitizers, sylvestre.ledru

Differential Revision: https://reviews.llvm.org/D53601

llvm-svn: 345625