examples/c: Fix compile issus with -j20.

More than one building task of the libbpf and bpftool will be created
with -j20. For the libbpf, several same install step running at the
same time will cause the compiling error.

See the issus: #354

To solve this, change the dependencies of the external project "xxx"
from "xxx-build" to "xxx".

Signed-off-by: weipeng <[email protected]>

Author: weipeng

examples/c/CMakeLists.txt

@@ -83,7 +83,7 @@ foreach(app ${apps})
 
   # Build object skeleton and depend skeleton on libbpf build
   bpf_object(${app_stem} ${app_stem}.bpf.c)
-  add_dependencies(${app_stem}_skel libbpf-build bpftool-build)
+  add_dependencies(${app_stem}_skel libbpf bpftool)
 
   add_executable(${app_stem} ${app_stem}.c)
   target_link_libraries(${app_stem} ${app_stem}_skel)