package.py: skip dwarfsrcfiles for Clang LTO static libraries

package.py: skip dwarfsrcfiles for Clang LTO static libraries

When using Clang toolchain with LTO enabled, static libraries (.a) contain
LLVM bitcode objects instead of ELF objects. dwarfsrcfiles cannot process
these files and fails with "not a valid ELF file" error.

Rather than catching the error message, guard the dwarfsrcfiles call by
checking for the specific conditions: static library (using is_static_lib()
magic check) + clang toolchain + lto in DISTRO_FEATURES. When all conditions
are met, skip the call silently.

Signed-off-by: mark.yang <mark.yang@lge.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>