[CMake] Adding another missing include. NFC.
[CMake] Adding another missing include. NFC.

This also works fine today, but will break with my upcoming refactoring.

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@267941 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt