Fix some issues reported by Valgrind

* Update the target suppression file.
* Disable the detection of mismatched free() / delete / delete []
calls, since it results in a lot of false positives (a known
Valgrind limitation associated with asymmetric inlining of
operator new() and operator delete()).
* Avoid a memory leak in the code generator tests, caused by the
fact that the VIXL-based ARM code generator does not always use
the arena allocator.
* Fix an access to uninitialized memory.

Test: m valgrind-test-art-target
Test: valgrind --leak-check=full --show-mismatched-frees=no \
               --ignore-range-below-sp=1024-1 \
               --suppressions=valgrind-target-suppressions.txt \
               dalvikvm ...
Change-Id: I891a3247aa9828226b4e62c69d6e1c8398d757b8