chore: emit //go:build instead of // +build (#10)

Author: Yi Duan

asm2asm.py

@@ -2494,15 +2494,15 @@ def main():
 
     # convert the original sources
     if OUTPUT_RAW:
-        asm.out.append('// +build amd64')
+        asm.out.append('//go:build amd64')
         asm.out.append('// Code generated by asm2asm, DO NOT EDIT.')
         asm.out.append('')
         asm.out.append('package %s' % pkg)
         asm.out.append('')
         ## native text
         asm.out.append('var Text%s = []byte{' % STUB_NAME)
     else:
-        asm.out.append('// +build !noasm !appengine')
+        asm.out.append('//go:build !noasm !appengine')
         asm.out.append('// Code generated by asm2asm, DO NOT EDIT.')
         asm.out.append('')
         asm.out.append('#include "go_asm.h"')