Use specified exception mask for buildinfo

This way we only catch exceptions which we're intended to
and if something bad happens (like missing import due to
refactor or so) we'll see them instantly.

build_files/scons/tools/Blender.py

@@ -414,7 +414,7 @@ def buildinfo(lenv, build_type):
     if os.path.isdir(os.path.abspath('.git')):
         try:
             build_commit_timestamp = subprocess.check_output(args=['git', 'log', '-1', '--format=%ct']).strip()
-        except:
+        except OSError:
             build_commit_timestamp = None
         if not build_commit_timestamp:
             # Git command not found

build_files/scons/tools/btools.py

@@ -58,7 +58,7 @@ def get_version():
 def get_hash():
     try:
         build_hash = subprocess.check_output(['git', 'rev-parse', '--short', 'HEAD']).strip()
-    except:
+    except OSError:
         build_hash = None
         print("WARNING: could not use git to retrieve current Blender repository hash...")
     if build_hash == '' or build_hash == None: