ClangCompleter tests not built when no libclang

When the user doesn't want semantic completion with clang, then tests that test
those features are not included in the test binary.

cpp/ycm/CMakeLists.txt

@@ -26,8 +26,14 @@ option( PATH_TO_LLVM_ROOT "Path to the root of a LLVM+Clang binary distribution"
 option( USE_SYSTEM_LIBCLANG "Set to ON to use the system libclang library" OFF )
 option( EXTERNAL_LIBCLANG_PATH "Path libclang library to use" )
 
-if ( NOT PATH_TO_LLVM_ROOT AND NOT USE_SYSTEM_LIBCLANG AND NOT
+if ( PATH_TO_LLVM_ROOT OR USE_SYSTEM_LIBCLANG OR EXTERNAL_LIBCLANG_PATH )
-    EXTERNAL_LIBCLANG_PATH )
+  set( USE_CLANG_COMPLETER TRUE )
+endif()
+
+if ( USE_CLANG_COMPLETER AND
+     NOT PATH_TO_LLVM_ROOT AND
+     NOT USE_SYSTEM_LIBCLANG AND
+     NOT EXTERNAL_LIBCLANG_PATH )
   message( FATAL_ERROR
     "You have not specified which libclang to use. You have several options:\n"
     " 1. Set PATH_TO_LLVM_ROOT to a path to the root of a LLVM+Clang binary "

cpp/ycm/tests/CMakeLists.txt

@@ -45,6 +45,14 @@ link_directories(
 
 file( GLOB SOURCES *.h *.cpp )
 
+if ( NOT USE_CLANG_COMPLETER )
+  file( GLOB_RECURSE to_remove_clang ClangCompleter/*.h ClangCompleter/*.cpp )
+
+  if( to_remove_clang )
+    list( REMOVE_ITEM SOURCES ${to_remove_clang} )
+  endif()
+endif()
+
 add_executable( ${PROJECT_NAME}
                 ${SOURCES}
               )