fontconfig 2.14 doesn't compile with CentOS toolchain

The usual

../src/fcserialize.c: In function ‘FcSerializeFind’:
../src/fcserialize.c:123:5: error: ‘for’ loop initial declarations are only allowed in C99 mode
     for (size_t n = 0; n < buckets_count; ++n) {
     ^

Would need a --std=c99 at least. The previous version < 2.14 compiled fine.