Fix small typo in Block ABI docs

[dmaclach]

Summary

I think the C++ code example had the wrong name for the block copy function.

[jroelofs]

can you please upload the patch with more context?

git show -U9999 <sha>

[rjmccall]

LGTM

clang/docs/Block-ABI-Apple.rst

struct __block_literal_10 {
         struct __block_descriptor_10 *descriptor;
         const FOO foo;
     };
     
     void __block_invoke_10(struct __block_literal_10 *_block) {
        printf("%d\n", _block->foo.value());
     }
     
-    void __block_literal_10(struct __block_literal_10 *dst, struct __block_literal_10 *src) {
+    void __block_copy_10(struct __block_literal_10 *dst, struct __block_literal_10 *src) {
          FOO_ctor(&dst->foo, &src->foo);
     }
     
     void __block_dispose_10(struct __block_literal_10 *src) {
          FOO_dtor(&src->foo);
     }
     
     static struct __block_descriptor_10 {