build: simplify the condition in the repl build (NFC)
build: simplify the condition in the repl build (NFC)

Fold a `if(cond)` followed with an `if(NOT cond)` set into a single set.
NFC.

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb