libz-sys armv7s-apple-ios warnings

gistfile1.txt

$ cargo build --release --target=armv7s-apple-ios
   Compiling pkg-config v0.3.14
   Compiling cc v1.0.25
   Compiling libc v0.2.43
   Compiling libz-sys v1.0.21 (file:///Users/jot/libz-sys)
warning: src/zlib/gzlib.c:214:15: warning: implicitly declaring library function 'snprintf' with type 'int (char *, unsigned long, const char *, ...)' [-Wimplicit-function-declaration]
warning:         (void)snprintf(state->path, len + 1, "%s", (const char *)path);
warning:               ^
warning: src/zlib/gzlib.c:214:15: note: include the header <stdio.h> or explicitly provide a declaration for 'snprintf'
warning: 1 warning generated.
warning: src/zlib/gzwrite.c:428:11: warning: implicitly declaring library function 'vsnprintf' with type 'int (char *, unsigned long, const char *, __builtin_va_list)' [-Wimplicit-function-declaration]
warning:     len = vsnprintf(next, state->size, format, va);
warning:           ^
warning: src/zlib/gzwrite.c:428:11: note: include the header <stdio.h> or explicitly provide a declaration for 'vsnprintf'
warning: 1 warning generated.
    Finished release [optimized] target(s) in 7.90s