Clang update.py: enable debug info for ToT builds

tools/clang/scripts/update.py

Index: tools/clang/scripts/update.py
diff --git a/tools/clang/scripts/update.py b/tools/clang/scripts/update.py
index a719649702c0a031fd5d3791c45bb451d76d42ee..279ed579e5209fee1f1d74997ea0984df3baa17d 100755
--- a/tools/clang/scripts/update.py
+++ b/tools/clang/scripts/update.py
@@ -470,7 +470,6 @@ def UpdateClang(args):
   ldflags = []
 
   base_cmake_args = ['-GNinja',
-                     '-DCMAKE_BUILD_TYPE=Release',
                      '-DLLVM_ENABLE_ASSERTIONS=ON',
                      '-DLLVM_ENABLE_THREADS=OFF',
                      '-DLLVM_ENABLE_TIMESTAMPS=OFF',
@@ -478,6 +477,13 @@ def UpdateClang(args):
                      '-DLLVM_USE_CRT_RELEASE=MT',
                      ]
 
+  if use_head_revision:
+    # For ToT builds, which are used to catch compiler bugs early, enable debug
+    # info for better backtraces when crashing.
+    base_cmake_args += ['-DCMAKE_BUILD_TYPE=RelWithDebInfo']
+  else:
+    base_cmake_args += ['-DCMAKE_BUILD_TYPE=Release']
+
   binutils_incdir = ''
   if sys.platform.startswith('linux'):
     binutils_incdir = os.path.join(BINUTILS_DIR, 'Linux_x64/Release/include')
@@ -652,11 +658,13 @@ def UpdateClang(args):
     # If any Chromium tools were built, install those now.
     RunCommand(['ninja', 'cr-install'], msvc_arch='x64')
 
-  if sys.platform == 'darwin':
-    # See http://crbug.com/256342
-    RunCommand(['strip', '-x', os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')])
-  elif sys.platform.startswith('linux'):
-    RunCommand(['strip', os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')])
+  if not use_head_revision:
+    # Strip the binaries to save size, except for ToT builds.
+    if sys.platform == 'darwin':
+      # See http://crbug.com/256342
+      RunCommand(['strip', '-x', os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')])
+    elif sys.platform.startswith('linux'):
+      RunCommand(['strip', os.path.join(LLVM_BUILD_DIR, 'bin', 'clang')])
 
   # TODO(thakis): Check that `clang --version` matches VERSION.