scons: Allow clean non-interactive builds

On a clean build, the git tool will wait for input() before installing
git hooks. Allow bypassing this via a command-line flag, making it
possible to perform a clean build non-interactively.

Bug: 199780674
Test: build_gem5 --install-hooks
Change-Id: I48be2c1a7c2335a2f4f6359adf582ca8b0ae5939
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/50410
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

site_scons/site_tools/git.py

@@ -42,6 +42,7 @@ import os
 import sys
 
 import gem5_scons.util
+import SCons.Script
 
 git_style_message = """
 You're missing the gem5 style or commit message hook. These hooks help
@@ -99,11 +100,14 @@ def install_style_hooks(env):
         return
 
     print(git_style_message, end=' ')
-    try:
-        input()
-    except:
-        print("Input exception, exiting scons.\n")
-        sys.exit(1)
+    if SCons.Script.GetOption('install-hooks'):
+        print("Installing revision control hooks automatically.")
+    else:
+        try:
+            input()
+        except:
+            print("Input exception, exiting scons.\n")
+            sys.exit(1)
 
     git_style_script = env.Dir("#util").File("git-pre-commit.py")
     git_msg_script = env.Dir("#ext").File("git-commit-msg")