configure.ac: drop -gsplit-dwarf from llvm-config --cxxflags output
Apparently, Ubuntu compiles clang with -gsplit-dwarf.
This results in -gsplit-dwarf appearing in the output of
llvm-config --cxxflags and subsequently causing *.dwo files
to be generated. These do not get cleaned by "make mostlyclean" and
therefore cause "make distcheck" to fail.
Remove the flag from the llvm-config --cxxflags output
to avoid these files getting generated.
An alternative would be to clean up the files, by adding
MOSTLYCLEANFILES = $(am_libpet_la_OBJECTS:$(OBJEXT)=dwo)
to Makefile.am.
Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>