Fix build on musl by including stdint.h

[Calandracas606]

openmp fails to build on musl since it lacks the defines for int32_t

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[Calandracas606]

Ping

[mstorsjo]

The change itself looks good to me, but I'm not sure if this library has any other specific conventions, so looping in @shiltian as well.

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[shiltian]

Do we want to use C header here instead of the C++ one?

[Calandracas606]

it looks like both the C and C++ headers are used (sometimes both! see omptarget.h), but the C++ one appears to be more common.

I could open a new PR changing to the C++ header if preferred

[shiltian]

Yeah, a patch to unify those headers would be great.

[MaskRay]

/cherry-pick 45fe67d

[llvmbot]

/pull-request #82897