Fix: libcrmcommon: use uint32_t for 32-bit magic numbers
So that they are correctly handled on 32-bit systems.
Previously unit test would fail on 32-bit systems:
> lib/common/tests/xml/crm_xml_init_test TAP version 13 1..8 ok 1 - buffer_scheme_test not ok 2 - create_document_node # 0xffffffff81726354 != 0x81726354 # crm_xml_init_test.c:61: error: Failure!