fix building on Win7

[rfomin]

Fix #1848

[MrAlaux]

Late reply, but it works: I can compile without issues again, and the build launches just fine. Thanks!

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Unrelated, but while we're on it, I guess I could mention that I do get the following warning:

E:\woof-master\spng\spng.c: In function 'spng__inflate_init':
E:\woof-master\spng\spng.c:1212:13: note: '#pragma message: inflateValidate() not available, SPNG_CTX_IGNORE_ADLER32 will be ignored'
 1212 |     #pragma message ("inflateValidate() not available, SPNG_CTX_IGNORE_ADLER32 will be ignored")
      |             ^~~~~~~

No idea of what it means.

[fabiangreffrath]

It is completely irrelevant for us.

randy408/libspng#270

[MrAlaux]

I should've mentioned this before, but the only thing that was impeding compilation on my end was the CREATE_WAITABLE_TIMER_HIGH_RESOLUTION flag; the rest of the CreateWaitableTimerEx() call didn't raise any errors or warnings. Why exactly do we add a condition for the whole thing instead of just for the flag?

[rfomin]

Why exactly do we add a condition for the whole thing instead of just for the flag?

We need CreateWaitableTimerEx just because of this flag. There is CreateWaitableTimer below, which works fine.

We can place the #ifdef HAVE_HIRES_TIMER macro differently, but technically there is no difference.