NASM: Fix object format when CXX is enabled but not C

Check CXX data pointer size if C is not set.

Modules/CMakeASM_NASMInformation.cmake

@@ -8,19 +8,25 @@ set(CMAKE_ASM_NASM_SOURCE_FILE_EXTENSIONS nasm asm)
 
 if(NOT CMAKE_ASM_NASM_OBJECT_FORMAT)
   if(WIN32)
-    if(CMAKE_C_SIZEOF_DATA_PTR EQUAL 8)
+    if(DEFINED CMAKE_C_SIZEOF_DATA_PTR AND CMAKE_C_SIZEOF_DATA_PTR EQUAL 8)
+      set(CMAKE_ASM_NASM_OBJECT_FORMAT win64)
+    elseif(DEFINED CMAKE_CXX_SIZEOF_DATA_PTR AND CMAKE_CXX_SIZEOF_DATA_PTR EQUAL 8)
       set(CMAKE_ASM_NASM_OBJECT_FORMAT win64)
     else()
       set(CMAKE_ASM_NASM_OBJECT_FORMAT win32)
     endif()
   elseif(APPLE)
-    if(CMAKE_C_SIZEOF_DATA_PTR EQUAL 8)
+    if(DEFINED CMAKE_C_SIZEOF_DATA_PTR AND CMAKE_C_SIZEOF_DATA_PTR EQUAL 8)
+      set(CMAKE_ASM_NASM_OBJECT_FORMAT macho64)
+    elseif(DEFINED CMAKE_CXX_SIZEOF_DATA_PTR AND CMAKE_CXX_SIZEOF_DATA_PTR EQUAL 8)
       set(CMAKE_ASM_NASM_OBJECT_FORMAT macho64)
     else()
       set(CMAKE_ASM_NASM_OBJECT_FORMAT macho)
     endif()
   else()
-    if(CMAKE_C_SIZEOF_DATA_PTR EQUAL 8)
+    if(DEFINED CMAKE_C_SIZEOF_DATA_PTR AND CMAKE_C_SIZEOF_DATA_PTR EQUAL 8)
+      set(CMAKE_ASM_NASM_OBJECT_FORMAT elf64)
+    elseif(DEFINED CMAKE_CXX_SIZEOF_DATA_PTR AND CMAKE_CXX_SIZEOF_DATA_PTR EQUAL 8)
       set(CMAKE_ASM_NASM_OBJECT_FORMAT elf64)
     else()
       set(CMAKE_ASM_NASM_OBJECT_FORMAT elf)