To avoid installing header files needed by clang to disk
(/usr/share/bcc), embed the files as strings inside the library and feed
them to clang as memory buffers. The mechanism that we use to do this
retains all of the existing features, as in one can still do `#include
<bcc/helpers.h>`, even though it is redundant, and clang will pick up
the embedded file.

Fixes: #333
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>