fixup! component/default: system gcc can be used only if all gcc, g++ and...

fixup! component/default: system gcc can be used only if all gcc, g++ and gfortran exist and their versions are same.

component/defaults.cfg

@@ -40,7 +40,7 @@ part = gcc-10.5
 # slapos.rebootstrap (see https://bugs.python.org/issue34112 about Python 3.7+).
 min_version = 5.4
 init =
-  import os, subprocess
+  import errno, os, subprocess
   parse_version = lambda ver: tuple(map(int, ver.strip().split('.')))
   version_set = set()
   for command in ('gcc', 'g++', 'gfortran'):
@@ -51,7 +51,9 @@ init =
     except subprocess.CalledProcessError: # BBB: old GCC
       version = subprocess.check_output((command, '-dumpversion'),
                                         universal_newlines=True).strip()
-    except FileNotFoundError:
+    except OSError as e:
+      if e.errno != errno.ENOENT:
+        raise
       version = None
     version_set.add(version)
   if None in version_set or len(version_set) != 1: