Revert "Create a clean environment to invoke find_package(BZip2)"

This reverts commit 174be33091457332dd2fc42c905d0de029f54257.
Revert "Only find BZip2 if we're not using cmbzip2."

This reverts commit e03ff536ded3fd36bbbe5367129309ff5602dde0.
Treat non-imported targets as library names.
Merge topic 'try_compile-targets' into next

a96e1ae Treat non-imported targets as library names.
72d207b Revert "Only find BZip2 if we're not using cmbzip2."
03a9211 Revert "Create a clean environment to invoke find_package(BZip2)"