[libunwind][cmake] Add an option to enable/disable tests

libunwind/CMakeLists.txt

 option(LIBUNWIND_ENABLE_SHARED "Build libunwind as a shared library." ON)
 option(LIBUNWIND_ENABLE_STATIC "Build libunwind as a static library." ON)
 option(LIBUNWIND_ENABLE_CROSS_UNWINDING "Enable cross-platform unwinding support." OFF)
 option(LIBUNWIND_ENABLE_ARM_WMMX "Enable unwinding support for ARM WMMX registers." OFF)
 option(LIBUNWIND_ENABLE_THREADS "Build libunwind with threading support." ON)
 option(LIBUNWIND_WEAK_PTHREAD_LIB "Use weak references to refer to pthread functions." OFF)
 option(LIBUNWIND_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF)
 option(LIBUNWIND_INCLUDE_DOCS "Build the libunwind documentation." ${LLVM_INCLUDE_DOCS})
+option(LIBUNWIND_INCLUDE_TESTS "Build the libunwind tests." ${LLVM_INCLUDE_TESTS})
 option(LIBUNWIND_IS_BAREMETAL "Build libunwind for baremetal targets." OFF)
 option(LIBUNWIND_USE_FRAME_HEADER_CACHE "Cache frame headers for unwinding. Requires locking dl_iterate_phdr." OFF)
 option(LIBUNWIND_REMEMBER_HEAP_ALLOC "Use heap instead of the stack for .cfi_remember_state." OFF)
 
 set(LIBUNWIND_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBUNWIND_INSTALL_LIBRARY "Install the libunwind library." ON)
 cmake_dependent_option(LIBUNWIND_INSTALL_STATIC_LIBRARY

 include_directories(include)
 
 add_subdirectory(src)
 
 if (LIBUNWIND_INCLUDE_DOCS)
   add_subdirectory(docs)
 endif()
 
-if (EXISTS ${LLVM_CMAKE_PATH})
+if (LIBUNWIND_INCLUDE_TESTS AND EXISTS ${LLVM_CMAKE_PATH})
   add_subdirectory(test)
 endif()