FC23 and FC24 need Clang 3.9.0 because of ABI changes in the C++
runtime library. Split the installation instructions to FC22 and
FC23/24.
### Install binary clang
```
+# FC22
wget http://llvm.org/releases/3.7.1/clang+llvm-3.7.1-x86_64-fedora22.tar.xz
sudo tar xf clang+llvm-3.7.1-x86_64-fedora22.tar.xz -C /usr/local --strip 1
+
+# FC23 and FC24
+wget http://llvm.org/releases/3.9.0/clang+llvm-3.9.0-x86_64-fedora23.tar.xz
+sudo tar xf clang+llvm-3.9.0-x86_64-fedora23.tar.xz -C /usr/local --strip 1
```
### Install and compile BCC