Enable arm64 optimizations that exist for power/x86 (#3393)

	* Enable unaligned accesses on arm64

	64-bit Arm platforms support unaligned accesses.

	Running the string benchmarks this change improves performance
	by an average of 1.04x, min .96x, max 1.21x, median 1.01x

	* arm64 enable gc optimizations

	Similar to x86 and powerpc optimizations.

	|       |compare-ruby|built-ruby|
	|:------|-----------:|---------:|
	|hash1  |       0.225|     0.237|
	|       |           -|     1.05x|
	|hash2  |       0.110|     0.110|
	|       |       1.00x|         -|

	* vm_exec.c: improve performance for arm64

	|                               |compare-ruby|built-ruby|
	|:------------------------------|-----------:|---------:|
	|vm_array                       |     26.501M|   27.959M|
	|                               |           -|     1.06x|
	|vm_attr_ivar                   |     21.606M|   31.429M|
	|                               |           -|     1.45x|
	|vm_attr_ivar_set               |     21.178M|   26.113M|
	|                               |           -|     1.23x|
	|vm_backtrace                   |       6.621|     6.668|
	|                               |           -|     1.01x|
	|vm_bigarray                    |     26.205M|   29.958M|
	|                               |           -|     1.14x|
	|vm_bighash                     |    504.155k|  479.306k|
	|                               |       1.05x|         -|
	|vm_block                       |     16.692M|   21.315M|
	|                               |           -|     1.28x|
	|block_handler_type_iseq        |       5.083|     7.004|
	|                               |           -|     1.38x|
	---
	 gc.c                           | 13 +++++++++++++
	 gc.h                           |  2 ++
	 include/ruby/internal/config.h |  2 ++
	 regint.h                       |  2 +-
	 siphash.c                      |  2 +-
	 st.c                           |  2 +-
	 vm_exec.c                      |  8 ++++++++
	 7 files changed, 28 insertions(+), 3 deletions(-)

Apply __attribute__((__returns_nonnull__)) when available.

clang also supports __attribute__((__alloc_size__)) so why not use
it when the compiler says it does.

Make them gcc friendly.  Note that realloc canot be __malloc__
attributed, according to the GCC manual.

See also https://rubyci.org/logs/rubyci.s3.amazonaws.com/centos6/ruby-master/log/20190910T003005Z.fail.html.gz

* include/ruby/defines.h: introduce "COLDFUNC" function attribute
  on several compilers for called unlikely functions.
  Apply to rb_memerror, rb_warn and rb_bug.

  A patch form  methodmissing <lourens@bearmetal.eu>.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66228 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

on most of platforms except mswin.

Changing it to static was needed for mswin because it doesn't use
transform_mjit_header, but for platforms that use it, it causes link
error like:

/usr/bin/ld: /tmp/_ruby_mjit_p21652u0.o: relocation R_X86_64_PC32 against undefined symbol `rb_vm_search_method_slowpath' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: Bad value
collect2: error: ld returned 1 exit status

include/ruby/defines.h: MJIT_FUNC_EXPORTED moved to intern.h

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64942 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

[Bug #13496]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64630 b2dd03c8-39d4-4d8f-98ff-823fe69b080e