Fix if statement and tabbing in analysis makefile

Sorry about this, just a few hours after !745 (merged) got merged...

There's an error in the makefile, that causes problems in the case --enable-onnx is false. I did check this case, but we must have tweaked it again after that check.

Two things are wrong:

• Tabbing matters in the makefile, and though it looked right if it were a bash script, it fails as it stands.
• As far as I can work out, make doesn't like redefinitions - autoconf spits out a warning in the previous case with just tabbing corrected. So I've gone with the seperate if-else block definitions, which is one extra line of code, but doesn't produce a warning message, and means there's zero ambiguity about what's going on.