eliminate libc dependence of libdrpreload.so

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on December 04, 2013 12:28:42_

xref issue #46 We should be able to remove these, many just by linking with string.c:

> nm lib64/debug/libdrpreload.so | grep ' U '
U atoi@@GLIBC_2.2.5
U dynamorio_app_init
U dynamorio_app_take_over
U dynamorio_set_envp
U fprintf@@GLIBC_2.2.5
U get_application_short_name
U getenv@@GLIBC_2.2.5
U memmove@@GLIBC_2.2.5
U memset@@GLIBC_2.2.5
U snprintf@@GLIBC_2.2.5
U stderr@@GLIBC_2.2.5
U strchr@@GLIBC_2.2.5
U strcmp@@GLIBC_2.2.5
U strlen@@GLIBC_2.2.5
U strncpy@@GLIBC_2.2.5
U strstr@@GLIBC_2.2.5

_Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1334_