llvm-cov: Handle missing source files as GCOV does

If the source files referenced by a gcno file are missing, gcov
outputs a coverage file where every line is simply /*EOF*/.  This also
occurs for lines in the coverage that are past the end of a file that
is found.

This change mimics gcov.

llvm-svn: 208149
diff --git a/llvm/test/tools/llvm-cov/Inputs/test_missing.output b/llvm/test/tools/llvm-cov/Inputs/test_missing.output
new file mode 100644
index 0000000..ada0c36
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/test_missing.output
@@ -0,0 +1,8 @@
+File 'srcdir/./nested_dir/../test.h'
+Lines executed:100.00% of 1
+srcdir/./nested_dir/../test.h:creating 'test.h.gcov'
+
+File 'srcdir/./nested_dir/../test.cpp'
+Lines executed:84.21% of 38
+srcdir/./nested_dir/../test.cpp:creating 'test.cpp.gcov'
+