Improve the rtld-elf testcases

- Address the implied libm dependency [*]
- Fix compilation [warnings/errors] with various WARNS levels, clang, and gcc

[*] Found by: make tinderbox with MK_TESTS == yes on arm/armeb

Sponsored-by: EMC / Isilon Storage Division
Use WARNS=3 with gcc (4.6 complains about -Wcast-qual)

Sponsored-by: EMC / Isilon Storage Division
Merge branch 'isilon-atf' of https://github.com/yaneurabeya/freebsd into isilon-atf