[libc++abi] Fix typo in CMake error message

Author: ldionne

libcxxabi/CMakeLists.txt

@@ -48,7 +48,7 @@ option(LIBCXXABI_ENABLE_PEDANTIC "Compile with pedantic enabled." OFF)
 option(LIBCXXABI_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." ON)
 if (LIBCXXABI_USE_LLVM_UNWINDER AND NOT "libunwind" IN_LIST LLVM_ENABLE_RUNTIMES)
-  message(FATAL_ERROR "LIBCXXABI_USE_LLVM_UNWINDER is set to ON, but libuwnind is not specified in LLVM_ENABLE_RUNTIMES.")
+  message(FATAL_ERROR "LIBCXXABI_USE_LLVM_UNWINDER is set to ON, but libunwind is not specified in LLVM_ENABLE_RUNTIMES.")
 endif()
 option(LIBCXXABI_ENABLE_STATIC_UNWINDER "Statically link the LLVM unwinder." OFF)
 option(LIBCXXABI_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF)