lttng-ust: fix do_compile error when PACKAGECONFIG examples is enabled

when PACKAGECONFIG enabled examples, compile failed with error:
fix below compile error during PACKGAGECONFIG examples is enabled:
tmp/work/corei7-64-wrs-linux/lttng-ust/2_2.13.0-r0/recipe-sysroot-native/usr/bin/x86_64-wrs-linux/../../libexec/x86_64-wrs-linux/gcc/x86_64-wrs-linux/11.2.0/ld: warning: liblttng-ust-common.so.1, needed by ../../../src/lib/lttng-ust/.libs/liblttng-ust.so, not found (try using -rpath or -rpath-link)
tmp/work/corei7-64-wrs-linux/lttng-ust/2_2.13.0-r0/recipe-sysroot-native/usr/bin/x86_64-wrs-linux/../../libexec/x86_64-wrs-linux/gcc/x86_64-wrs-linux/11.2.0/ld: warning: liblttng-ust-tracepoint.so.1, needed by ../../../src/lib/lttng-ust/.libs/liblttng-ust.so, not found (try using -rpath or -rpath-link)

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>