Build errors in Xcode 9 beta 3+ -- implicit declaration of function 'check_string' and 'check' are invalid in C99

[jaclync]

Pods/Google-Diff-Match-Patch/DiffMatchPatchCFUtilities.c:391:5: error: implicit declaration of function 'check_string' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
    check_string(hash <= diff_UniCharMax, "Hash value has exceeded UniCharMax!");
    ^
Pods/Google-Diff-Match-Patch/DiffMatchPatchCFUtilities.c:634:5: error: implicit declaration of function 'check' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
    check(status == 0);
    ^
2 errors generated.

• cocoapods
• version 0.0.1
• reproducible in Xcode 9 beta 3 and above, including Xcode 9 GM seed