libc: implement some FORTIFY_SOURCE functions

Add initial support for -D_FORTIFY_SOURCE to bionic for the
following functions:

* memcpy
* memmove
* strcpy
* strcat
* strncpy
* strncat

This change adds a new version of the above functions which passes
the size of the destination buffer to __builtin___*_chk.

If the compiler can determine, at compile time, that the destination
buffer is large enough, or the destination buffer can point to an object
of unknown size, then the check call is bypassed.

If the compiler can't make a compile time decision, then it calls
the __*_chk() function, which does a runtime buffer size check

These options are only enabled if the code is compiled with
-D_FORTIFY_SOURCE=1 or 2, and only when optimizations are enabled.

Please see

for additional details on FORTIFY_SOURCE.

Testing: Compiled the entire Android tree with -D_FORTIFY_SOURCE=1,
and verified that everything appears to be working properly.
Also created a test buffer overflow, and verified that it was
caught by this change.

Change-Id: I4fddb445bafe92b16845b22458d72e6dedd24fbc
8 files changed