add predicates for @os_error.OSError

[Guest0x0]

add predicates for testing some commonly used error code on @os_error.OSError. Once we get target OS #cfg in the future, this can be replaced by const.

[coveralls]

Pull Request Test Coverage Report for Build 698

Details

• 8 of 13 (61.54%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.1%) to 78.189%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/fs/utils.mbt	2	7	28.57%

Files with Coverage Reduction	New Missed Lines	%
src/fs/utils.mbt	3	65.38%

Totals
Change from base Build 697:	0.1%
Covered Lines:	1183
Relevant Lines:	1513

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💛 - Coveralls