fix portability issue in error handling of build_triple

Author: binarycrusader

src/bootstrap/bootstrap.py

@@ -315,7 +315,7 @@ def build_triple(self):
         try:
             ostype = subprocess.check_output(['uname', '-s']).strip().decode(default_encoding)
             cputype = subprocess.check_output(['uname', '-m']).strip().decode(default_encoding)
-        except subprocess.CalledProcessError:
+        except (subprocess.CalledProcessError, OSError):
             if sys.platform == 'win32':
                 return 'x86_64-pc-windows-msvc'
             err = "uname not found"