elfutils: use PRIVATE_LIBS for the ptest package

EXCLUDE_PACKAGES_FROM_SHLIBS is too broad: it suppresses both generation
of required and provided shlibs. We need to suppress only the provided shlibs
(to avoid clashes with the main package providing the same shlibs),
and run the required shlib dependencies generator as usual.

(From OE-Core rev: 7d342fd04266bedc12706c111c5b83d952566bca)

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/elfutils/elfutils_0.176.bb

@@ -142,4 +142,4 @@ INHIBIT_PACKAGE_STRIP_FILES = "\
     ${PKGD}${PTEST_PATH}/backends/libebl_x86_64.so \
 "
 
-EXCLUDE_PACKAGES_FROM_SHLIBS = "${PN}-ptest"
+PRIVATE_LIBS_${PN}-ptest = "libdw.so.1 libelf.so.1"