Solve false negative for various malloc replaced functions arguments

The replacement functions are running on the simulated CPU.
The code on the simulated CPU does not necessarily use
all arguments. E.g. args can be ignored and/or only given
to a NON SIMD call.
The definedness of such 'unused' arguments will not be verified
by memcheck.
A call to 'trigger_memcheck_error_if_undefined' allows 
memcheck to detect such errors for the otherwise unused args.
Apart of allowing memcheck to detect an error, the function
trigger_memcheck_error_if_undefined has no effect and
has a minimal cost for other tools replacing malloc functions.

(suggestion of the 'no operation check' from Julian).

tested on f12/x86, debian6/amd64, f18/ppc64
Note that some Darwin specific code has been modified
in coregrind/m_replace_malloc/vg_replace_malloc.c.
(Some of) this code has not been compiled (no access to a
Darwin system). The code changed is trivial, so there is
some chance it will compile and even maybe work.

Added a new test verifying that various malloc related
functions undefined args are triggering an error in memcheck.




git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13361 a5019735-40e9-0310-863c-91ae7b9d1cf9