Enable `LIBOQS_DIR` as cache entry and environment variable. #264

Job	Run time
cygwin (windows-2019, win64, -DOQS_ALGS_ENABLED=STD)	6m 40s
msvc (windows-2019, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A-masm)	3m 5s
msvc_native (windows-2019, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A, .CMake/too...	4m 19s
msvc_native (windows-2019, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A, .CMake/too...	4m 14s
msvc_native (windows-2022, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A, .CMake/too...	4m 20s
msvc_native (windows-2022, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A, .CMake/too...	4m 8s
	26m 46s

Provide feedback