[libc++] NFC: Remove unused CMake option

That option seems to be a remnant that has now been replaced by the
LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_SHARED_LIBRARY setting.

Fixes PR45347.

Author: ldionne

libcxx/CMakeLists.txt

@@ -207,7 +207,6 @@ option(LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS
 # Build libc++abi with libunwind. We need this option to determine whether to
 # link with libunwind or libgcc_s while running the test cases.
 option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." OFF)
-option(LIBCXXABI_ENABLE_STATIC_UNWINDER "Statically link the LLVM unwinder." OFF)
 
 # Target options --------------------------------------------------------------
 option(LIBCXX_BUILD_32_BITS "Build 32 bit libc++." ${LLVM_BUILD_32_BITS})