Imath.half_c_only failure on windows

Testing it on Windows Version 10.0.19045 Build 19045, x86 environment via syswow, and using cl from Visual Studio 2022 Community Edition, one of the test fails.

I attach the full output of all tests.

Global test status is:
```
C:\Users\jddfr\git\Imath-build>nmake test

Microsoft (R) Program Maintenance Utility Version 14.32.31332.0
Copyright (C) Microsoft Corporation. Tous droits réservés.

Running tests...
Test project C:/Users/jddfr/git/Imath-build
Start 1: Imath.half_c_only
1/36 Test #1: Imath.half_c_only .......................***Failed 0.03 sec
Start 2: Imath.testToFloat
2/36 Test #2: Imath.testToFloat ....................... Passed 0.02 sec
Start 3: Imath.testSize
3/36 Test #3: Imath.testSize .......................... Passed 0.01 sec
Start 4: Imath.testArithmetic
4/36 Test #4: Imath.testArithmetic .................... Passed 0.01 sec
Start 5: Imath.testNormalizedConversionError
5/36 Test #5: Imath.testNormalizedConversionError ..... Passed 1.97 sec
Start 6: Imath.testDenormalizedConversionError
6/36 Test #6: Imath.testDenormalizedConversionError ... Passed 1.93 sec
Start 7: Imath.testRoundingError
7/36 Test #7: Imath.testRoundingError ................. Passed 0.21 sec
Start 8: Imath.testBitPatterns
8/36 Test #8: Imath.testBitPatterns ................... Passed 0.01 sec
Start 9: Imath.testClassification
9/36 Test #9: Imath.testClassification ................ Passed 0.01 sec
Start 10: Imath.testLimits
10/36 Test #10: Imath.testLimits ........................ Passed 0.01 sec
Start 11: Imath.testHalfLimits
11/36 Test #11: Imath.testHalfLimits .................... Passed 0.01 sec
Start 12: Imath.testFunction
12/36 Test #12: Imath.testFunction ...................... Passed 0.02 sec
Start 13: Imath.testVec
13/36 Test #13: Imath.testVec ........................... Passed 0.01 sec
Start 14: Imath.testColor
14/36 Test #14: Imath.testColor ......................... Passed 0.01 sec
Start 15: Imath.testShear
15/36 Test #15: Imath.testShear ......................... Passed 0.01 sec
Start 16: Imath.testMatrix
16/36 Test #16: Imath.testMatrix ........................ Passed 0.01 sec
Start 17: Imath.testMiscMatrixAlgo
17/36 Test #17: Imath.testMiscMatrixAlgo ................ Passed 3.08 sec
Start 18: Imath.testRoots
18/36 Test #18: Imath.testRoots ......................... Passed 0.01 sec
Start 19: Imath.testFun
19/36 Test #19: Imath.testFun ........................... Passed 0.01 sec
Start 20: Imath.testInvert
20/36 Test #20: Imath.testInvert ........................ Passed 0.01 sec
Start 21: Imath.testInterval
21/36 Test #21: Imath.testInterval ...................... Passed 0.01 sec
Start 22: Imath.testFrustum
22/36 Test #22: Imath.testFrustum ....................... Passed 0.07 sec
Start 23: Imath.testRandom
23/36 Test #23: Imath.testRandom ........................ Passed 2.32 sec
Start 24: Imath.testExtractEuler
24/36 Test #24: Imath.testExtractEuler .................. Passed 4.82 sec
Start 25: Imath.testExtractSHRT
25/36 Test #25: Imath.testExtractSHRT ................... Passed 0.60 sec
Start 26: Imath.testQuat
26/36 Test #26: Imath.testQuat .......................... Passed 0.01 sec
Start 27: Imath.testQuatSetRotation
27/36 Test #27: Imath.testQuatSetRotation ............... Passed 2.06 sec
Start 28: Imath.testQuatSlerp
28/36 Test #28: Imath.testQuatSlerp ..................... Passed 1.91 sec
Start 29: Imath.testLineAlgo
29/36 Test #29: Imath.testLineAlgo ...................... Passed 0.06 sec
Start 30: Imath.testBoxAlgo
30/36 Test #30: Imath.testBoxAlgo ....................... Passed 5.64 sec
Start 31: Imath.testBox
31/36 Test #31: Imath.testBox ........................... Passed 0.01 sec
Start 32: Imath.testProcrustes
32/36 Test #32: Imath.testProcrustes .................... Passed 0.03 sec
Start 33: Imath.testTinySVD
33/36 Test #33: Imath.testTinySVD ....................... Passed 0.02 sec
Start 34: Imath.testJacobiEigenSolver
34/36 Test #34: Imath.testJacobiEigenSolver ............. Passed 3.17 sec
Start 35: Imath.testFrustumTest
35/36 Test #35: Imath.testFrustumTest ................... Passed 0.01 sec
Start 36: Imath.testInterop
36/36 Test #36: Imath.testInterop ....................... Passed 0.01 sec

97% tests passed, 1 tests failed out of 36

Total Test time (real) = 28.33 sec

The following tests FAILED:
1 - Imath.half_c_only (Failed)
Errors while running CTest
Output from these tests are in: C:/Users/jddfr/git/Imath-build/Testing/Temporary/LastTest.log
Use "--rerun-failed --output-on-failure" to re-run the failed cases verbosely.
NMAKE : fatal error U1077: 'echo' : code retour '0x8'
Stop.
```

[LastTest.log](https://github.com/AcademySoftwareFoundation/Imath/files/10147170/LastTest.log)

Start with Testing/Temporary/LastTest.log and rerun the Imath.half_c_only test with CTest's --rerun-failed --output-on-failure options on the reported Windows x86 environment. Compare its failure with the 35 passing tests and determine what is needed for this test to pass; done means the test passes and the full suite reports no failures.

Written by the indexing model from the issue text.