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|

1 files changed, 13 insertions, 0 deletions

diff --git a/gc.c b/gc.c
index 22972dfc80..788f06f158 100644
--- a/gc.c
+++ b/gc.c
@@ -1115,6 +1115,19 @@ tick(void)
     return val;
 }
 
+#elif defined(__aarch64__) &&  defined(__GNUC__)
+typedef unsigned long tick_t;
+#define PRItick "lu"
+
+static __inline__ tick_t
+tick(void)
+{
+    unsigned long val;
+    __asm__ __volatile__ ("mrs %0, cntvct_el0", : "=r" (val));
+    return val;
+}
+
+
 #elif defined(_WIN32) && defined(_MSC_VER)
 #include <intrin.h>
 typedef unsigned __int64 tick_t;