bcc: and generated compat/linux/bpf.h to .gitignore

For package builds, compat/linux/bpf.h is generated from
compat/linux/virtual_bpf.h, so add it to .gitignore.

Suggested-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>

Author: alan-maguire

.gitignore

@@ -16,3 +16,6 @@ examples/cgroupid/cgroupid
 # Output from docker builds
 scripts/docker/output/
 /output/
+
+# UAPI header generated for libbpf package-based builds
+src/cc/compat/linux/bpf.h