Give generated assembly files different names for arm and aarch64.

Change-Id: I843e43ec56e14a2697bbdd5d6093fdb4d7cf15c2
Reviewed-on: https://boringssl-review.googlesource.com/5200
Reviewed-by: Adam Langley <agl@google.com>

util/generate_build_files.py

@@ -434,6 +434,9 @@ def WriteAsmFiles(perlasms):
       if not output.startswith('src'):
         raise ValueError('output missing src: %s' % output)
       output = os.path.join(outDir, output[4:])
+      if output.endswith('-armx.${ASM_EXT}'):
+        output = output.replace('-armx',
+                                '-armx64' if arch == 'aarch64' else '-armx32')
       output = output.replace('${ASM_EXT}', asm_ext)
 
       if arch in ArchForAsmFilename(filename):