Build: configure: fix overkill format specifier serving uint64_t check

This was a chained mess:

• fixed-width integer types from <stdint.h> are usually accompanied with respective format specifiers in <inttypes.h>, which should have been a first line of the solution

• relying on the compiler erroring out on the incorrect format specifier in a compile test is broken (if nothing else, may fail like that for unrelated reasons, which also happened in the case referred below), especially since it's trivially solvable in a preprocessing test, which avoids inteferring with -D_FORTIFY_SOURCE vs. optimization switches -- even more so when they are split between CFLAGS and CPPFLAGS, see https://bugs.clusterlabs.org/show_bug.cgi?id=5274