mac: Create all parent directories of build/mac_files/xcode_binaries

After https://chromium-review.googlesource.com/c/chromium/src/+/1745443,
build/mac_files might not yet exist, so create that too.
https://bugs.chromium.org/p/chromium/issues/detail?id=992510#c12 suggests
that this is necessary.

Bug: 992510,991431,984746
Change-Id: If1fecf20d69185efe0f789b5437f9ee508737bde
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1747191
Commit-Queue: Nico Weber <[email protected]>
Commit-Queue: Stephen Martinis <[email protected]>
Auto-Submit: Nico Weber <[email protected]>
Reviewed-by: Stephen Martinis <[email protected]>
Cr-Commit-Position: refs/heads/master@{#685777}
diff --git a/build/mac_toolchain.py b/build/mac_toolchain.py
index 776b379..ea62f280 100755
--- a/build/mac_toolchain.py
+++ b/build/mac_toolchain.py
@@ -94,7 +94,7 @@
   # also ensures that there will be no conflicts of cipd root.
   binaries_root = os.path.join(TOOLCHAIN_ROOT, 'xcode_binaries')
   if not os.path.exists(binaries_root):
-    os.mkdir(binaries_root)
+    os.makedirs(binaries_root)
 
   # 'cipd ensure' is idempotent.
   args = [