FORTIFY_SOURCE: remove memcpy overlap checks

These checks haven't been as useful as I hoped, and it's
causing a false positive finding.  Remove the overlap
compile time checks.

Change-Id: I5d45dde10ae4663d728230d41fa904adf20acaea
Tests for string routines.

Change-Id: I24068a228f59df1c3b758c5b2026a09720490616
Signed-off-by: Anna Tikhonova <anna.tikhonova@intel.com>
glibc 2.15 treats errno as signed in strerror(3).

And the only reason I hadn't done that in bionic is because I wanted to behave
the same as glibc.

Change-Id: I2cf1bf0aac82a748cd6305a2cabbac0790058570
Add stack canaries / strcpy tests.

Add a test to ensure that stack canaries are working
correctly. Since stack canaries aren't normally generated
on non-string functions, we have to enable stack-protector-all.

Add a test to ensure that an out of bounds strcpy generates
a runtime failure.

Change-Id: Id0d3e59fc4b9602da019e4d35c5c653e1a57fae4
fix strerror_r test

e6e60065ff093ff8c859ab146cf543531cb1967c modified strerror_r to
treat errno as signed. However, the change to the test code
modified the "strerror" test, not the "strerror_r" test.

Make the same change for the strerror_r code.

Change-Id: Ia236a53df5745935e229a4446a74da8bed0cfd7b
FORTIFY_SOURCE: optimize

Don't do the fortify_source checks if we can determine, at
compile time, that the provided operation is safe.

This avoids silliness like calling fortify source on things like:

  size_t len = strlen("asdf");
  printf("%d\n", len);

and allows the compiler to optimize this code to:

  printf("%d\n", 4);

Defer to gcc's builtin functions instead of pointing our code
to the libc implementation.

Change-Id: I5e1dcb61946461c4afaaaa983e39f07c7a0df0ae

Conflicts:

	libc/include/string.h
Simple google3-compatible benchmarking.

Based on our open-source RE2 benchmarking code.

Includes benchmarks for a handful of <string.h> functions.

Change-Id: I30eb70d25dbf4ad5f2ca44976a8ce3b1ff7dad01
Add a memmove(3) benchmark.

Change-Id: I9c0ffae0b5aae29521b7e68e5ce2318b5a401cba