[llvm] test-release.sh: Only build the clang target in stage 1 and 2 (PR #72703)

[Tom Stellard via llvm-commits]

tstellar wrote:

Your probably thinking of: 19f100e89ad5b62e1fca76bd9c3aceca173cb45e.  This commit stopped building all the other projects like lld, lldb, etc., but it still was building with the default target which included tests, utilities and other things that aren't actually used in the later phases.

https://github.com/llvm/llvm-project/pull/72703