[llvm-cov] Use the native path in the coverage report.

The coverage reports contain the source or binary file paths. On Windows, 
the file path might contain the seperators of both '/' and '\'. This patch 
uses the native path in the coverage reports. For example, on Windows, 
all '/' are converted to '\'.

Differential Revision: https://reviews.llvm.org/D23922

llvm-svn: 280061
diff --git a/llvm/test/tools/llvm-cov/double_dots.c b/llvm/test/tools/llvm-cov/double_dots.c
index 2c79a6ec..9f4b7c1 100644
--- a/llvm/test/tools/llvm-cov/double_dots.c
+++ b/llvm/test/tools/llvm-cov/double_dots.c
@@ -5,6 +5,8 @@
 // RUN: llvm-profdata merge %S/Inputs/double_dots.proftext -o %t.profdata
 // RUN: llvm-cov show %S/Inputs/double_dots.covmapping -instr-profile=%t.profdata -o %t.dir
 // RUN: FileCheck -input-file=%t.dir/index.txt %s
+// RUN: llvm-cov show -format=html %S/Inputs/double_dots.covmapping -instr-profile=%t.profdata -o %t.dir
+// RUN: FileCheck -input-file=%t.dir/index.html %s
 
 // CHECK-NOT: coverage{{.*}}dots{{.*}}..{{.*}}dots