[lldb] Bump SWIG minimum version to 4

SWIG 4 was released in 2019 and has been the de-facto standard for a
while now. All bots are running SWIG 4.0 or later.

This was motivated by #64279 which discovered that 662548c8 broke the
LLDB build with SWIG 3 on Windows.

Differential revision: https://reviews.llvm.org/D156804