Revert "lit: Move RUN at line comment after the command."

This reverts commit 8d3dc1e.

Test needs to be updated.

Author: pcc

llvm/docs/CommandGuide/lit.rst

@@ -100,7 +100,7 @@ OUTPUT OPTIONS
 
  Each command is printed before it is executed. This can be valuable for
  debugging test failures, as the last printed command is the one that failed.
- Moreover, :program:`lit` inserts ``'RUN: at line N'`` after each
+ Moreover, :program:`lit` inserts ``'RUN: at line N'`` before each
  command pipeline in the output to help you locate the source line of
  the failed command.
 

llvm/utils/lit/lit/TestRunner.py

@@ -1231,7 +1231,7 @@ def executeScript(test, litConfig, tmpBase, commands, cwd):
                 # the shell's execution trace for the 'set' commands by
                 # redirecting their stderr to /dev/null.
                 if command:
-                    msg = f"{shlex.quote(command.lstrip())} \\# '{dbg}'"
+                    msg = f"'{dbg}': {shlex.quote(command.lstrip())}"
                 else:
                     msg = f"'{dbg}' has no command after substitutions"
                 commands[i] = (