The ordering pair, and the two-file alternative

Answer

make > build.log 2>&1 make 2>&1 > build.log make > build.out 2> build.err

Line 1 puts everything in build.log. Line 2 puts only the output there and leaves errors on your screen. Line 3 sidesteps the question entirely by naming two files, so no descriptor is duplicated.

S&K 3e ch9 §9.6–9.9, §9.13