[libunwind][CMake] Fix name of LIBUNWIND_SUPPORTS_NODEFAULTLIBS_FLAG

The CMake variable LIBUNWIND_SUPPORTS_NODEFAULTLIBS_FLAG has been renamed
into C_SUPPORTS_NODEFAULTLIBS_FLAG because the last one is used in the
confix-ix.cmake file while the variable with the original name is not used
at al.

Differential Revision: https://reviews.llvm.org/D126466

GitOrigin-RevId: e251fb4cdeb723eff5507be1efeb3fc69f7a2ce7
diff --git a/cmake/config-ix.cmake b/cmake/config-ix.cmake
index f716532..c9b65b3 100644
--- a/cmake/config-ix.cmake
+++ b/cmake/config-ix.cmake
@@ -35,7 +35,7 @@
 if (CXX_SUPPORTS_NOSTDLIBXX_FLAG)
   set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nostdlib++")
 else()
-  llvm_check_compiler_linker_flag(C "-nodefaultlibs" LIBUNWIND_SUPPORTS_NODEFAULTLIBS_FLAG)
+  llvm_check_compiler_linker_flag(C "-nodefaultlibs" C_SUPPORTS_NODEFAULTLIBS_FLAG)
   if (C_SUPPORTS_NODEFAULTLIBS_FLAG)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nodefaultlibs")
   endif()