Use array indexing with considering clang's feeling

```
In file included from sprintf.c:1256:
./vsnprintf.c:833:8: warning: adding 'int' to a string does not append to the string [-Wstring-plus-int]
                            IS_PRI_EXTRA_MARK(fmt)) {
                            ^~~~~~~~~~~~~~~~~~~~~~
./vsnprintf.c:826:34: note: expanded from macro 'IS_PRI_EXTRA_MARK'
           strncmp((s)+1, PRI_EXTRA_MARK+1, \
                          ~~~~~~~~~~~~~~^~
./vsnprintf.c:833:8: note: use array indexing to silence this warning
./vsnprintf.c:826:34: note: expanded from macro 'IS_PRI_EXTRA_MARK'
           strncmp((s)+1, PRI_EXTRA_MARK+1, \
                                        ^
1 warning generated.
```

0 files changed, 0 insertions, 0 deletions