[libc++] Properly handle environment variables with '=' in them

Cr-Mirrored-From: https://chromium.googlesource.com/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 0feaf22c8a7c68d758306733e6d80bcdefd91658
diff --git a/utils/run.py b/utils/run.py
index 33d0095..3e9a470 100644
--- a/utils/run.py
+++ b/utils/run.py
@@ -12,9 +12,10 @@
 program's error code.
 """
 
+import argparse
+import os
 import subprocess
 import sys
-import argparse
 
 
 def main():
@@ -39,7 +40,7 @@
             return rc
 
     # Extract environment variables into a dictionary
-    env = {k : v  for (k, v) in map(lambda s: s.split('='), args.env)}
+    env = {k : v  for (k, v) in map(lambda s: s.split('=', 1), args.env)}
 
     # Ensure the file dependencies exist
     for file in args.dependencies: