Add benchmarking of forward and backward unaligned memmoves.

On some microarchitectures performance of the backwards memmove improves
if the stores use STR with decreasing addresses.

This fix is similar to the one done one glibc (beea361050).

Optimize strlen using a mix of scalar and SIMD code. On modern micro
architectures large strings are 55% faster than the current version,
and 35% faster than strlen-mte.  On the random strlen benchmark the
speedup is 3.4% and 40% respectively.

Add strlen benchmark with a random latency and small/medium throughput tests.

If limit is near SIZE_MAX it can overflow in the mutually aligned path.
Fix this by clamping limit to SIZE_MAX.

Improve the previous fix - if a string is immediately preceded by a NUL byte
and the first byte is 0x1, it may be confused by the NUL check as a NUL byte.
Instead of removing bytes outside the string via a shift, force them to be
non-NUL.

* New functionality (64-bit Arm)
  * string: Optimized MTE variants of strlen, strnlen, strchr,
    strchrnul, strrchr, memchr, memrchr, strcpy, stpcpy, strcmp,
    strncmp
  * string: Changes to support BTI
  * string: New optimized memrchr, strnlen
* Performance improvements (Neoverse N1)
  * strchr/strchrnul: 21% improvement on long strings
  * strrchr: 11% improvement
  * strnlen: 130% improvement on long strings, 50% on short strings
* Benchmark and tests
  * string: New memcpy benchmark
  * string: Cleanup testsuite and improve test coverage

Ensure nul bytes before unaligned strings are correctly ignored.

Improve strcmp performance. On various micro architectures the speedup is 65%
on large unaligned strings and 21% on large (mutually) aligned strings.
On small unaligned strings the speedup is 12%.

Print results in bytes/ns. Add medium and large copy benchmark.

Set taggs for every test case so that boundaries are as narrow as
possible. There is no handling of tag faults, so the test will
crash if there is a MTE problem.

The implementations that are not compatible are excluded, including
the standard symbols that may come from an mte incompatible libc.

Clean up code and improve test coverage.

Clean up code and improve test coverage.

Clean up code and improve test coverage.

Cleanup stpcpy test and improve test coverage.

Cleanup strcpy test and improve test coverage.

Cleanup strnlen test and improve test coverage.

Cleanup strlen test and improve test coverage.

Add optimized MTE-compatible strcpy-mte and stpcpy-mte. On various micro
architectures the speedup over the non-MTE version is 53% on large strings
and 20-60% on small strings.

Improve strrchr performance by using a fast strchr loop to find the first
match. On various micro architectures the speedup is 30-80% on large strings
and 32% on small strings.

Add GNU property notes to asm files in asmdefs.h instead of adding
the END_FILE macro to each file.

The WANT_GNU_PROPERTY macro can be still used to opt-out from the
notes.

Add new memrchr test.

Add optimized MTE-comparible memrchr. This walks the input backwards
using the same algorithm as memchr-mte.

Improve strlen performance by using a much simpler SIMD implementation.
On various micro architectures the speedup is 11% on large strings and
63% on small strings.

Improve memchr test coverage and cleanup code.

Improve strnlen test coverage and cleanup code.

Improve memchr performance by using a more efficient termination test.
On various micro architectures the speedup is 16% on large strings and
46% on small strings.

Improve strnlen performance by using a much simpler SIMD implementation.
On modern micro architectures the speedup is 2.3x on large strings and
1.5x on small strings.

Use the GNU style consistently in the string test code.

Added clang-format guard comments where necessary so the
code can be reformated using the clang-format tool and
GNU style settings from gcc contrib/clang-format.

GNU Property Notes are only supported in recent tooling and older
tools may warn about them, so it makes sense to remove these notes
on a system where BTI is not supported anyway.

The actual BTI instructions should be kept in place to avoid
disturbing code layout.

-DWANT_GNU_PROPERTY=0 removes the .note.gnu.property section
from assembly files (ideally it would be based on the compiler
default setting, but there is no feature test macro for BTI and
PAC-RET).

Remove 2 more instructions, resulting in a 9.8% speedup of medium
sized strings (16-32).

The BTI patch changed ENTRY so the loops got misaligned, this fixes
that regression.

Remove 2 more instructions, resulting in a 6.8% speedup of medium
sized strings (16-32).

The BTI patch changed ENTRY so the loops got misaligned, this fixes
that regression.

Reading outside the range of the string is only allowed within 16 byte
aligned granules when MTE is enabled.

This implementation is based on string/aarch64/strncmp.S

Change the case when strings are are misaligned, align the pointers
down, and ignore bytes before the start of the string. Carry the part
that is not compared to the next comparison.

Testing done:
string/test/strncmp.c on big endian, little endian and with MTE support.
Booted nanodroid with MTE enabled.

Bechmarked on Pixel4.

Reading outside the range of the string is only allowed within 16 byte
aligned granules when MTE is enabled.

This implementation is based on string/aarch64/strcmp.S

Change the case when strings are are misaligned, align the pointers
down, and ignore bytes before the start of the string. Carry the part
that is not compared to the next comparison.

Testing done:
optimized-routines/string/test/strcmp.c on big and little endian.
Booted nanodroid with MTE enabled.
bionic string tests with MTE enabled.

Benchmarks results:
Run both bionic benchmarks and glibc benchmarks on Pixel4. Cores A76 and A55.

This change addds the landing pads to the start of functions
implemented in assembly, by adding it to the ENTRY macro. To avoid
skipping it when using an alias, every ENTRY_ALIAS use must precede
the corresponding ENTRY.

Furthermore, the GNU property note is added to the assembly
files. Since none of the functions save LR to stack, both BTI and PAC
support are indicated.

Paddings before __strncmp_aarch64 and __strnlen_aarch64 were adjusted.

Reading outside the range of the string is only allowed within
16 byte aligned granules when MTE is enabled.

This implementation is based on string/aarch64/strrchr.S.

Testing done:
optimized-routines/string/test/strrchr.c
Booted nanodroid with MTE enabled.
Bionic string tests with MTE enabled.
Big endian with Qemu: qemu-aarch64_be

Improve strchrnul performance by using more efficient termination tests.
On various micro architectures the speedup is 20% on large strings and 26%
on small strings.

Improve strchr performance by using a more efficient termination test.
On various micro architectures the speedup is 19% on large strings and
19% on small strings.

Improve strrchr performance by using a more efficient termination test.
On various micro architectures the speedup is 11% on large strings.