CMake: Don't install llvm-tblgen twice
CMake: Don't install llvm-tblgen twice

Summary:
The add_tablegen macros defines its own install target, and it was also calling
add_llvm_utility which adds another install target.

Configuring with -DLLVM_TOOLS_INSTALL_DIR set to something other than
'bin' along with -DLLVM_INSTALL_UTILS=ON was causing llvm-tablgen
to be installed to two separate directories.

Reviewers: beanz, hans

Reviewed By: beanz

Subscribers: llvm-commits, mgorny

Differential Revision: https://reviews.llvm.org/D30656

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@297403 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm