[llvm-cov] Relax a test for Windows

Attempt to address this bot failure:

  http://bb.pgr.jp/builders/ninja-clang-i686-msc19-R/builds/4967

llvm-svn: 275522

llvm/test/tools/llvm-cov/double_dots.c

@@ -19,4 +19,4 @@ int main() {}
 // Check that we get the right error when writing to an invalid path:
 
 // RUN: not llvm-cov show %S/Inputs/double_dots.covmapping -instr-profile=%t.profdata -o /dev/null 2>&1 | FileCheck %s -check-prefix=ERROR-MESSAGE
-// ERROR-MESSAGE: error: Not a directory: Could not create index file!
+// ERROR-MESSAGE: error: {{.*}}: Could not create index file!