cu_varint warnings

[robe]

cu_varint.c
cu_varint.c: In function 'do_test_u32_varint':
cu_varint.c:30:2: warning: implicit declaration of function 'varint_u32_encoded_size' [-Wimplicit-function-declaration]
  size = varint_u32_encoded_size(nr);
  ^
cu_varint.c:35:2: warning: implicit declaration of function 'varint_u32_encode_buf' [-Wimplicit-function-declaration]
  varint_u32_encode_buf(nr, buf);
  ^
cu_varint.c: In function 'do_test_s32_varint':
cu_varint.c:50:2: warning: implicit declaration of function 'varint_s32_encoded_size' [-Wimplicit-function-declaration]
  size = varint_s32_encoded_size(nr);
  ^
cu_varint.c:55:2: warning: implicit declaration of function 'varint_s32_encode_buf' [-Wimplicit-function-declaration]
  varint_s32_encode_buf(nr, buf);
  ^
cu_varint.c: In function 'do_test_u64_varint':
cu_varint.c:70:2: warning: implicit declaration of function 'varint_u64_encoded_size' [-Wimplicit-function-declaration]
  size = varint_u64_encoded_size(nr);
  ^
cu_varint.c:75:2: warning: implicit declaration of function 'varint_u64_encode_buf' [-Wimplicit-function-declaration]
  varint_u64_encode_buf(nr, buf);
  ^
cu_varint.c: In function 'do_test_s64_varint':
cu_varint.c:90:2: warning: implicit declaration of function 'varint_s64_encoded_size' [-Wimplicit-function-declaration]
  size = varint_s64_encoded_size(nr);
  ^
cu_varint.c:95:2: warning: implicit declaration of function 'varint_s64_encode_buf' [-Wimplicit-function-declaration]
  varint_s64_encode_buf(nr, buf);
  ^
cu_varint.c: In function 'test_varint':
cu_varint.c:154:2: warning: this decimal constant is unsigned only in ISO C90 [enabled by default]
  do_test_s32_varint(-2147483648, 5, "FFFFFFFF0F");
  ^