clang update.py: move the code for building into build.py

Over time update.py has become a really complicated file. This is a step
towards simplifying things by making update.py be a script focused on updating
and build.py on building.

Bug: 884608
Change-Id: I4d65a2416f39e832b685495bd53cbe284f97967a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1571628
Commit-Queue: Hans Wennborg <[email protected]>
Reviewed-by: Nico Weber <[email protected]>
Cr-Commit-Position: refs/heads/master@{#656007}
diff --git a/DEPS b/DEPS
index 8885ec3..051b8f4d 100644
--- a/DEPS
+++ b/DEPS
@@ -2408,7 +2408,7 @@
     'name': 'clang_tot',
     'pattern': '.',
     'condition': 'llvm_force_head_revision',
-    'action': ['python', 'src/tools/clang/scripts/update.py',
+    'action': ['python', 'src/tools/clang/scripts/build.py',
                '--llvm-force-head-revision',
                '--with-android={checkout_android}'],
   },