Revert "[profile] Hide lprofCurFilename"

This reverts commit r282294. It breaks a Linux bot:

  http://lab.llvm.org:8011/builders/clang-cmake-aarch64-42vma/builds/12180

It looks like the test checks that __llvm_profile_set_filename() alters the raw
profile filename in both the dylib and the main program. Now that
lprofCurFilename is hidden, this can't work, and we get two profiles (one for
the call to "main" and one for "func").

Back this change out so that we don't affect external users.

llvm-svn: 282304