Add ARM64 support

[jstasiak]

[jstasiak]

One thing I'm not sure about is the libstapsdt-x86_64.s assembly file. Everything seems to be working correctly with zero changes to that file, I guess the content is not really relevant and it's the minimum size of funcStart that matters?

Since I'm not familiar with this library's internals: does the size of funcStart matter if it's larger than current only x86-64? ARM64 NOPs are 4-byte wide:

root@ea6772147644:/libstapsdt# objdump -D build/lib/libstapsdt-x86_64.o                                                                                                                                             
                                                                                                                                                                                                                    
build/lib/libstapsdt-x86_64.o:     file format elf64-littleaarch64                                                                                                                                                  
                                                                                                                                                                                                                    
                                                                                                                                                                                                                    
Disassembly of section .text:                                                                                                                                                                                       
                                                                                                                                                                                                                    
0000000000000000 <_funcStart>:                                                                                                                                                                                      
   0:   d503201f        nop                                                                                                                                                                                         
   4:   d503201f        nop                                                                                                                                                                                         
   8:   d503201f        nop                                                                                                                                                                                         
   c:   d503201f        nop                                                                                                                                                                                         
  10:   d65f03c0        ret                                                                                                                                                                                         
                                                                                                                                                                                                                    
0000000000000014 <_funcEnd>:                                                                                                                                                                                        
  14:   d503201f        nop   
(...)
`