Warning: skipping dependency checks. ext/buffer.c: In function ‘cmark_strbuf_strrchr’: ext/buffer.c:220:3: error: ‘for’ loop initial declarations are only allowed in C99 mode for (bufsize_t i = pos; i >= 0; i--) { ^ ext/buffer.c:220:3: note: use option -std=c99 or -std=gnu99 to compile your code Error: Build error: Failed compiling object ext/buffer.o