Avoid redefining macros from different files.

[iphydf]

This change is 

[codecov]

Codecov Report

Merging #1104 into master will decrease coverage by 0.1%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1104      +/-   ##
==========================================
- Coverage   82.56%   82.46%   -0.11%     
==========================================
  Files          80       80              
  Lines       14316    14316              
==========================================
- Hits        11820    11805      -15     
- Misses       2496     2511      +15

Impacted Files	Coverage Δ
toxav/video.c	67.46% <ø> (ø)	⬆️
auto_tests/save_compatibility_test.c	87.93% <100%> (ø)	⬆️
auto_tests/set_name_test.c	93.61% <0%> (-6.39%)	⬇️
auto_tests/conference_simple_test.c	93.65% <0%> (-3.18%)	⬇️
toxav/msi.c	65.08% <0%> (-1.68%)	⬇️
toxav/toxav.c	67.85% <0%> (-1.47%)	⬇️
toxcore/onion_client.c	95.04% <0%> (-0.31%)	⬇️
toxcore/Messenger.c	86.01% <0%> (+0.16%)	⬆️
toxcore/net_crypto.c	93.6% <0%> (+0.57%)	⬆️
toxcore/LAN_discovery.c	84.9% <0%> (+0.94%)	⬆️

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[jhert0]

Reviewed 4 of 4 files at r1.
Reviewable status: 0 of 1 approvals obtained (waiting on @endoffile78)