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.
fix includes and shell commands for at86rf231
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
correct cc110x function names
Merge pull request #681 from OlegHahm/at86rf231_fixes

at86rf231: fix includes and shell commands
Merge pull request #684 from OlegHahm/avsextrem_spi_function_renaming

correct cc110x function names
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
Portable definition of function attributes
Merge pull request #689 from rousselk/compiler-attrib

Portable definition of function attributes