FindLibClang: add version 8.0.0_1

This commit adds the version string "8.0.0_1" to the list of LLVM
versions because the current version of LLVM in Homebrew (as of the
time of this commit) is version 8.0.0_1.

Another approach for detecting a macOS Homebrew install of the "llvm"
package (latest stable version) would be to add `/usr/local/opt/llvm`
to the list of search paths. Homebrew installs of older major versions
of LLVM are symlinked to paths of the form
`/usr/local/opt/llvm@${MAJOR_VERSION}` (e.g.,
`/usr/local/opt/llvm@7/`, `/usr/local/opt/llvm@6/`).

server/cmake/modules/FindLibClang.cmake

@@ -13,7 +13,7 @@
 # most recent versions come first
 # http://llvm.org/apt/
 set(LIBCLANG_KNOWN_LLVM_VERSIONS 9.0.0 9.0 9
-  8.0.0 8.0 8
+  8.0.0_1 8.0.0 8.0 8
   7.0.1 7.0.0 7.0 7
   6.0.1 6.0.0 6.0 6
   5.0.2 5.0.1 5.0.0 5.0 5