Fix compile errors with ENABLE_USDT=Off

Signed-off-by: Brenden Blanco <bblanco@gmail.com>

examples/CMakeLists.txt

@@ -2,7 +2,9 @@ set(EXAMPLE_PROGRAMS hello_world.py)
 install(PROGRAMS ${EXAMPLE_PROGRAMS} DESTINATION share/bcc/examples)
 
 if(ENABLE_CLANG_JIT)
+if(ENABLE_USDT)
 add_subdirectory(cpp)
+endif(ENABLE_USDT)
 add_subdirectory(lua)
 add_subdirectory(networking)
 add_subdirectory(tracing)

tests/cc/CMakeLists.txt

@@ -9,6 +9,7 @@ target_link_libraries(test_static bcc-static)
 
 add_test(NAME c_test_static COMMAND ${TEST_WRAPPER} c_test_static sudo ${CMAKE_CURRENT_BINARY_DIR}/test_static)
 
+if(ENABLE_USDT)
 add_executable(test_libbcc
 	test_libbcc.cc
 	test_c_api.cc
@@ -25,3 +26,4 @@ find_path(SDT_HEADER NAMES "sys/sdt.h")
 if (SDT_HEADER)
 	target_compile_definitions(test_libbcc PRIVATE HAVE_SDT_HEADER=1)
 endif()
+endif(ENABLE_USDT)