get rid of code that sets C_INCLUDE_PATH, LD_LIBRARY_PATH and LD_RUN_PATH for...

get rid of code that sets C_INCLUDE_PATH, LD_LIBRARY_PATH and LD_RUN_PATH for GMP, since it makes no difference w.r.t. the __gmp_get_memory_functions undefined references (real problem was that path of other libgmp.so was present in LD_LIBRARY_PATH)

add support to make LTO fully optional (required for GCC v4.5 build without libelf installed)