[lld][test] Fix use of escape character in an lld test on Windows

[lld][test] Fix use of escape character in an lld test on Windows

Summary:
Glob support was improved to accept `\` as an escape character in r375051, but reverted as r375052 due to a failure in this test on Windows.

The reason this failure seems Windows specific is because the path separator `\` is currently being relied on to be interpreted literally instead of as an escape character. Per documentation on linker input section wildcard patterns, this seems to be a bug in lld accepting `\` as a literal instead of an escape character.

For example:
```
SECTIONS{ .foo :{ /path/to/foo.o(.foo) }} # OK: standard UNIX path
SECTIONS{ .foo :{ C:/path/to/foo.o(.foo) }} # OK: windows accepts slashes in either direction
SECTIONS{ .foo :{ C:\\path\\to\\foo.o(.foo) }} # OK: escape character used to match a literal \
SECTIONS{ .foo :{ C:\path\to\foo.o(.foo) }} # BAD: this actually matches the path C:pathtofoo.o(.foo)
```

This avoids the problem in the test by using `%/T` in place of `%T` to normalize the path separator to `/`, which windows should also accept.

This patch just fixes the test, and glob support will be be relanded separately.

For a sample buildbot error, see: http://lab.llvm.org:8011/builders/clang-x64-windows-msvc/builds/11578/steps/stage%201%20check/logs/stdio

Reviewers: evgeny777, ruiu, MaskRay, espindola

Reviewed By: ruiu, MaskRay

Subscribers: emaste, arichardson, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69074

llvm-svn: 375126