Mesa doesn't build with current Scons version (3.1.0)

Submitted by Eric Engestrom @eric

Link to original bug (#111309)

Description

$ scons
scons: Reading SConscript files ...

scons: warning: EnsureSConsVersion is ignored for development version
File "SConstruct", line 33, in `<module>`
TypeError: a bytes-like object is required, not 'str':
  File "SConstruct", line 47:
    ENV = os.environ,
  File "/usr/lib/python3.7/site-packages/SCons/Environment.py", line 991:
    apply_tools(self, tools, toolpath)
  File "/usr/lib/python3.7/site-packages/SCons/Environment.py", line 107:
    env.Tool(tool)
  File "/usr/lib/python3.7/site-packages/SCons/Environment.py", line 1798:
    tool(self)
  File "/usr/lib/python3.7/site-packages/SCons/Tool/__init__.py", line 303:
    self.generate(env, *args, **kw)
  File "scons/gallium.py", line 219:
    env['gcc_compat'] = check_cc(env, 'GCC', 'defined(__GNUC__)')
  File "scons/gallium.py", line 135:
    source.write('#if !(%s)\n#error\n#endif\n' % expr)
  File "/usr/lib/python3.7/tempfile.py", line 481:
    return func(*args, **kwargs)

From the error, it sounds like it could be a python2 vs python3 issue?

It works fine if I downgrade back to scons 3.0.4 (which I'll be doing for the time being)