Revert "Improve cmake build for MSVC."

[iphydf]

This reverts commit f87f871.

Fixes #1201.

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This change is 

[sphaerophoria]

Reviewed 8 of 8 files at r1.
Reviewable status: 0 of 1 approvals obtained (waiting on @sphaerophoria)

[sphaerophoria]

Reviewable status: 0 of 1 approvals obtained

[sphaerophoria]

Reviewable status: 0 of 1 approvals obtained

[codecov]

Codecov Report

Merging #1203 into master will increase coverage by 0.1%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #1203     +/-   ##
========================================
+ Coverage    82.7%   82.9%   +0.1%     
========================================
  Files          82      82             
  Lines       14645   14646      +1     
========================================
+ Hits        12123   12146     +23     
+ Misses       2522    2500     -22

Impacted Files	Coverage Δ
toxav/msi.c	65.9% <ø> (+1.9%)	⬆️
toxcore/crypto_core_test.cc	90.3% <0%> (-9.7%)	⬇️
auto_tests/toxav_many_test.c	92.5% <0%> (-4.1%)	⬇️
toxcore/net_crypto.c	93.1% <0%> (-0.2%)	⬇️
toxcore/onion_client.c	95.9% <0%> (-0.2%)	⬇️
toxcore/DHT.c	76.6% <0%> (-0.1%)	⬇️
toxcore/Messenger.c	86.5% <0%> (-0.1%)	⬇️
toxav/toxav.c	68.2% <0%> (+0.4%)	⬆️
auto_tests/toxav_basic_test.c	83.5% <0%> (+1.9%)	⬆️
... and 2 more

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