Add handling of --no-as-needed linker flag to marley-config

[sjgardiner]

Venkatesh Iyer reports linker trouble building the example executables on Ubuntu. The cause appears to be the need to add -Wl,--no-as-needed to the compiler flags since the Ubuntu build of the GCC linker adds -Wl,--as-needed by default (see http://www.bnikolic.co.uk/blog/gnu-ld-as-needed.html). This is already done in the main MARLEY Makefile, but for the example programs it will be most convenient to handle at the marley-config level rather than requiring the user to add it manually.