"jobs=" settings are inheritted from slave configuration.
"-DCMAKE_C_FLAGS=" and "-DCMAKE_CXX_FLAGS=" for single-stage builds
are passed only to system compiler and don't affect behavior or results.
For two-stage bots (useTwoStage=True) these flags are preserved.
"-DLLVM_LIT_ARGS='-sv -j2'" flags are extraneous, testsuite runs fine
with default parallelism. We preserve "-DLLVM_PARALLEL_LINK_JOBS=2" for
linaro-tk1-* bots, which have only 2GB of RAM.