[gcov] Ignore blocks from another file
Constructs such as inline variables, #line, and #include can create
lexical blocks with a different filename.
GCOVProfiling and llvm-cov gcov currently don't handle such cases (see
GCOVLines::writeOut and GCOVFile::readGCNO) and would incorrectly
attribute the line number to the current file.
For now, ignore such blocks. Missing line execution counts is better
than wrong ones.
---
As a workaround that Apple targets don't use -mconstructor-aliases yet,
allow line execution count 4 on the A::A line (
1f34e282e8066281eb1447e21e44a2a2e9983e79).
(cherry picked from commit
406e81b79d26dae6838cc69d10a3e22635da09ef)