Bug 1571576 - Flush stderr before running subprocesses in build-clang. r=nalexander

Differential Revision: https://phabricator.services.mozilla.com/D40728

build/build-clang/build-clang.py

@@ -37,7 +37,7 @@ def symlink(source, link_name):
 
 
 def check_run(args):
-    print(' '.join(args), file=sys.stderr)
+    print(' '.join(args), file=sys.stderr, flush=True)
     if args[0] == 'cmake':
         # CMake `message(STATUS)` messages, as appearing in failed source code
         # compiles, appear on stdout, so we only capture that.