Fix bootstrap.py

Generate cfi_flags buildflags header in bootstrap.py and add comments to
base/BUILD.gn to try to prevent regressions.

Change-Id: I3da0817b4880d3f0ba732ead0a53d1b708258da8
Reviewed-on: https://chromium-review.googlesource.com/728379
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Peter Collingbourne <pcc@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#510552}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 29b1eb6e480f2fc250743d4eb572d3617c4a4e08

tools/gn/bootstrap/bootstrap.py

diff --git a/tools/gn/bootstrap/bootstrap.py b/tools/gn/bootstrap/bootstrap.py
index f154ed2..2f2dbaa 100755
--- a/tools/gn/bootstrap/bootstrap.py
+++ b/tools/gn/bootstrap/bootstrap.py
@@ -181,7 +181,15 @@
       {
           'ENABLE_LOCATION_SOURCE': 'false',
           'ENABLE_PROFILING': 'false',
-          'CAN_UNWIND_WITH_FRAME_POINTERS': 'false'
+          'CAN_UNWIND_WITH_FRAME_POINTERS': 'false',
+          'UNSAFE_DEVELOPER_BUILD': 'false'
+      })
+
+  write_buildflag_header_manually(root_gen_dir, 'base/cfi_flags.h',
+      {
+          'CFI_CAST_CHECK': 'false',
+          'CFI_ENFORCEMENT_TRAP': 'false',
+          'CFI_ENFORCEMENT_DIAGNOSTIC': 'false'
       })
 
   write_build_date_header(root_gen_dir)