Fix more warnings:

[comex]

• Externals/soundtouch/CMakeLists.txt: add -w (since it's not our code) to
  silence an unused variable warning
• Source/Core/Core/NetPlayClient.cpp: Work around a Clang/libc++ bug where
  initializing a std::array the way the standard says you're supposed to produces
  a warning. (libc++'s implementation of std::array, like any sane
  implementation, has a C array as a field, so the most explicit form of
  initialization would use two braces, one for the struct and one for the array.
  Clang has a general warning for not being explicit with braces, which is
  usually sane. But the standard only guarantees that initializing std::array
  works with a single pair of braces!) There are other places in Dolphin that
  incorrectly use double braces, presumably to avoid the warning, so maybe the
  warning should just be turned off, but in any case here I just switch to an
  equivalent .fill().

---

This change is