Fix potential error for sys.platform

This CL is to fix gap between python2.x and 3.x.
For python2.x: sys.platform returns 'linux2'
For python3.x: sys.platform returns 'linux'

python3.x(https://docs.python.org/3.6/library/sys.html#sys.platform)
python2.x(https://docs.python.org/2.7/library/sys.html#sys.platform)
Both 2.x and 3.x recommend to use 'startswith' to identify sys.platform.

Change-Id: Id5a0a007518b329d1320baf96ecf1164cd3ebec1
Signed-off-by: jiajia tang <tangjiajia@xiaomi.com>

tools/check_elf_file.py

@@ -72,9 +72,9 @@ ELF = collections.namedtuple(
 
 def _get_os_name():
   """Get the host OS name."""
-  if sys.platform == 'linux2':
+  if sys.platform.startswith('linux'):
     return 'linux'
-  if sys.platform == 'darwin':
+  if sys.platform.startswith('darwin'):
     return 'darwin'
   raise ValueError(sys.platform + ' is not supported')