bcc cmake error llvm-pdbdump does not exist

```
# cmake .. -DCMAKE_INSTALL_PREFIX=/usr
-- The C compiler identification is GNU 6.4.1
-- The CXX compiler identification is GNU 6.4.1
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Latest recognized Git tag is v0.3.0
-- Git HEAD is 9de830aec1ced10b038a26064bd3f1d62f874754
-- Revision is 0.3.0-9de830ae
-- Found BISON: /usr/bin/bison (found version "3.0.4")
-- Found FLEX: /usr/bin/flex (found version "2.6.0")
CMake Error at /usr/local/lib/cmake/llvm/LLVMExports.cmake:643 (message):
The imported target "llvm-pdbdump" references the file

"/usr/local/bin/llvm-pdbdump"

but this file does not exist. Possible reasons include:

* The file was deleted, renamed, or moved to another location.
* An install or uninstall procedure did not complete successfully.
* The installation package was faulty and contained

"/usr/local/lib/cmake/llvm/LLVMExports.cmake"

but not all the files it references.

Call Stack (most recent call first):
/usr/local/lib/cmake/llvm/LLVMConfig.cmake:143 (include)
CMakeLists.txt:22 (find_package)

-- Configuring incomplete, errors occurred!
```

Binaries for LLVM are available under /usr/local/bin/:
```
# /usr/local/bin/llc --version
LLVM (http://llvm.org/):
LLVM version 6.0.0git-fb0e1f5
Optimized build.
Default target: x86_64-unknown-linux-gnu
Host CPU: skylake

Registered Targets:
bpf - BPF (host endian)
bpfeb - BPF (big endian)
bpfel - BPF (little endian)
x86 - 32-bit X86: Pentium-Pro and above
x86-64 - 64-bit X86: EM64T and AMD64
```

Start with CMakeLists.txt at the find_package call and inspect /usr/local/lib/cmake/llvm/LLVMConfig.cmake and LLVMExports.cmake, along with the installed LLVM binaries. Reproduce the configuration error and determine why the exported llvm-pdbdump target points to a missing file; done means CMake configures successfully with the available LLVM installation.

Written by the indexing model from the issue text.