Fix #272: run `c_obj_create` under a lock. #329

Job	Run time
cygwin (windows-2019, win64, -DOQS_ALGS_ENABLED=STD)	6h 0m 10s
msvc (windows-2019, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A-masm)	1m 43s
msvc_native (windows-2019, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A, .CMake/too...	1s
msvc_native (windows-2022, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A, .CMake/too...	2m 33s
	6h 4m 27s

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