/usr/lib/llvm-3.5/build/autoconf/m4/ is in llvm-3.5-dev 1:3.5~svn201651-1ubuntu1.
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..
/usr/lib/llvm-3.5/build/autoconf/m4/build_exeext.m4
/usr/lib/llvm-3.5/build/autoconf/m4/c_printf_a.m4
/usr/lib/llvm-3.5/build/autoconf/m4/check_gnu_make.m4
/usr/lib/llvm-3.5/build/autoconf/m4/config_makefile.m4
/usr/lib/llvm-3.5/build/autoconf/m4/config_project.m4
/usr/lib/llvm-3.5/build/autoconf/m4/cxx_flag_check.m4
/usr/lib/llvm-3.5/build/autoconf/m4/define_subst.m4
/usr/lib/llvm-3.5/build/autoconf/m4/find_std_program.m4
/usr/lib/llvm-3.5/build/autoconf/m4/func_isinf.m4
/usr/lib/llvm-3.5/build/autoconf/m4/func_isnan.m4
/usr/lib/llvm-3.5/build/autoconf/m4/func_mmap_file.m4
/usr/lib/llvm-3.5/build/autoconf/m4/header_mmap_anonymous.m4
/usr/lib/llvm-3.5/build/autoconf/m4/huge_val.m4
/usr/lib/llvm-3.5/build/autoconf/m4/libtool.m4
/usr/lib/llvm-3.5/build/autoconf/m4/link_options.m4
/usr/lib/llvm-3.5/build/autoconf/m4/linux_mixed_64_32.m4
/usr/lib/llvm-3.5/build/autoconf/m4/ltdl.m4
/usr/lib/llvm-3.5/build/autoconf/m4/need_dev_zero_for_mmap.m4
/usr/lib/llvm-3.5/build/autoconf/m4/path_tclsh.m4
/usr/lib/llvm-3.5/build/autoconf/m4/rand48.m4
/usr/lib/llvm-3.5/build/autoconf/m4/sanity_check.m4
/usr/lib/llvm-3.5/build/autoconf/m4/single_cxx_check.m4
/usr/lib/llvm-3.5/build/autoconf/m4/visibility_inlines_hidden.m4