Fix -fno-delete-null-pointer-checks (#664)

Only use -fno-delete-null-pointer-checks if the supplied compiler knows
the flag. Clang does not understand the flag, and does not need it.
use pkg-config to add valgrind include path

makes knowledge of VALGRIND_VALGRIND_H vs. VALGRIND_H optional
update Makefiles to point to all-valgrind target

Header path knowledge is not necessary anymore
Merge pull request #664 from Kijewski/conditional-fno-delete-null-pointer-checks

clang does not know fno-delete-null-pointer-checks
Merge pull request #666 from LudwigOrtmann/native_valgrind_config

Native valgrind config