Fix build break for Clang builds.

Fix build break for Clang builds.

Summary:
Complains about

```
In file included from crypto/lib/cpp/CryptoException.cpp:1:
In file included from crypto/lib/cpp/CryptoException.h:5:
In file included from ./folly/Conv.h:30:
./folly/Range.h:573:19: error: redefinition of default argument
Comp eq = Comp()) {
^    ~~~~~~
./folly/Range.h:55:26: note: previous definition is here
Comp eq = Comp());
^    ~~~~~~
```

Redefinition of default arguments is not allowed in C++.

Test Plan:
```
fbconfig --clang admarket/adpublisher && fbmake dbg
```

contbuild, etc.

Reviewed By: lucian@fb.com

FB internal diff: D910800