only use 1 cpu

[xusk]

build from centos7 ; but only use 1 cpu

cmake -B build -DFAISS_ENABLE_GPU=OFF -DFAISS_ENABLE_C_API=ON -DBUILD_SHARED_LIBS=ON -DFAISS_ENABLE_PYTHON=ON -DFAISS_OPT_LEVEL=avx2 -DCMAKE_BUILD_TYPE=Release -DBLA_VENDOR=Intel10_64_dyn -DPython_EXECUTABLE=/usr/bin/python3 .

[chenjia123]

Add a build parameter：-j8

[chenjia123]

Add a build parameter：-j8

8 is num of core