rec: Backport 14550 to rec 5.1.x: json11: add include for cstdint

[omoerbeek]

fixes #14549, which came with a patch

(cherry picked from commit 8d6d32b)

Backport of #14550

Short description

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)
• checked that this code was merged to master

[coveralls]

Pull Request Test Coverage Report for Build 11346178886

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 36 unchanged lines in 6 files lost coverage.
• Overall coverage increased (+0.001%) to 66.404%

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Files with Coverage Reduction	New Missed Lines	%
pdns/iputils.cc	3	34.56%
pdns/remote_logger.cc	3	53.13%
pdns/recursordist/syncres.cc	4	79.67%
pdns/recursordist/test-syncres_cc1.cc	6	89.63%
pdns/recursordist/rec-tcpout.cc	6	50.79%
pdns/recursordist/rec-system-resolve.cc	14	43.87%

Totals
Change from base Build 11161224661:	0.001%
Covered Lines:	56908
Relevant Lines:	75723

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💛 - Coveralls