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.cpp.gcov b/llvm/test/tools/llvm-cov/Inputs/test_missing.cpp.gcov
new file mode 100644
index 0000000..1c138e4
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/test_missing.cpp.gcov
@@ -0,0 +1,77 @@
+        -:    0:Source:srcdir/./nested_dir/../test.cpp
+        -:    0:Graph:test_paths.gcno
+        -:    0:Data:test_paths.gcda
+        -:    0:Runs:3
+        -:    0:Programs:1
+        -:    1:/*EOF*/
+        -:    2:/*EOF*/
+        -:    3:/*EOF*/
+        -:    4:/*EOF*/
+        -:    5:/*EOF*/
+        -:    6:/*EOF*/
+        -:    7:/*EOF*/
+        -:    8:/*EOF*/
+        -:    9:/*EOF*/
+12884901888:   10:/*EOF*/
+        -:   11:/*EOF*/
+    #####:   12:/*EOF*/
+        -:   13:/*EOF*/
+        -:   14:/*EOF*/
+    #####:   15:/*EOF*/
+        -:   16:/*EOF*/
+        -:   17:/*EOF*/
+        -:   18:/*EOF*/
+        3:   19:/*EOF*/
+        3:   20:/*EOF*/
+        -:   21:/*EOF*/
+        -:   22:/*EOF*/
+        -:   23:/*EOF*/
+    #####:   24:/*EOF*/
+    #####:   25:/*EOF*/
+        -:   26:/*EOF*/
+        -:   27:/*EOF*/
+       12:   28:/*EOF*/
+       12:   29:/*EOF*/
+       12:   30:/*EOF*/
+        -:   31:/*EOF*/
+        -:   32:/*EOF*/
+       21:   33:/*EOF*/
+       36:   34:/*EOF*/
+       18:   35:/*EOF*/
+        3:   36:/*EOF*/
+        -:   37:/*EOF*/
+        -:   38:/*EOF*/
+        3:   39:/*EOF*/
+        -:   40:/*EOF*/
+        3:   41:/*EOF*/
+        3:   42:/*EOF*/
+        3:   43:/*EOF*/
+        3:   44:/*EOF*/
+        3:   45:/*EOF*/
+        3:   46:/*EOF*/
+    #####:   47:/*EOF*/
+    #####:   48:/*EOF*/
+        -:   49:/*EOF*/
+        -:   50:/*EOF*/
+       66:   51:/*EOF*/
+       30:   52:/*EOF*/
+        -:   53:/*EOF*/
+        6:   54:/*EOF*/
+        6:   55:/*EOF*/
+        -:   56:/*EOF*/
+        -:   57:/*EOF*/
+        3:   58:/*EOF*/
+        3:   59:/*EOF*/
+        -:   60:/*EOF*/
+        9:   61:/*EOF*/
+        9:   62:/*EOF*/
+        -:   63:/*EOF*/
+       12:   64:/*EOF*/
+       12:   65:/*EOF*/
+       30:   66:/*EOF*/
+        -:   67:/*EOF*/
+        3:   68:/*EOF*/
+25769803782:   69:/*EOF*/
+12884901888:   70:/*EOF*/
+        -:   71:/*EOF*/
+        3:   72:/*EOF*/