Usually with qmake we do it like this:

qmake Code:
  1. BUILD_FOR_CUST1 {
  2. DEFINES += "__COMPILE_FOR_CUST1__=1"
  3. }
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and if we want to activate the clause we write:

qmake Code:
  1. CONFIG += BUILD_FOR_CUST1
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or just call "qmake CONFIG+=BUILD_FOR_CUST1".

Alternatively you can use features (files with prf extension).