Make depot_tools scripts return exit codes properly on all platforms.

Changes:
1. Windows: exit /b %errorlevel% should be used instead of goto :EOF to get valid exit codes during cmd /c <script>.bat invocation.
2. Windows: delayed var expansion is required in update_depot_tools.bat exit code generation.
3. Posix: update_depot_tools returns exit code from update_git_repo function in case of a failure.

A rule of thumb on Windows: goto :EOF should not be used if %errorlevel% must be returned for all possible invocations.

Test case for update_depot_tools changes:
1. Make a change to depot_tools sources that will conflict with next depot_tools update
2. Run update_depot_tools either directly or via gclient
3. Expect a git error is triggered
4. Inspect %errorlevel% or $? depending on platform
5. Expected 1, but the actual result is 0.

Test case for changes in other .bat files:
1. Make a change to depot_tools sources that will conflict with next depot_tools update
2. Run cmd /c gclient
3. Expect a git error is triggered
4. Inspect %errorlevel%
5. Expected 1, but the actual result is 0.

Change-Id: I64459982bcd9cc3db1319a9b39224b7a7af8c5aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3688632
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Auto-Submit: Aleksey Khoroshilov <akhoroshilov@brave.com>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>

fetch.bat

@@ -7,8 +7,8 @@ setlocal
 :: Synchronize the root directory before deferring control back to gclient.py.
 call "%~dp0\update_depot_tools.bat"
 :: Abort the script if we failed to update depot_tools.
-IF %errorlevel% NEQ 0 (
+IF %ERRORLEVEL% NEQ 0 (
-  goto :EOF
+  exit /b %ERRORLEVEL%
 )
 
 :: Ensure that "depot_tools" is somewhere in PATH so this tool can be used

gclient.bat

@@ -10,8 +10,8 @@ IF "%DEPOT_TOOLS_UPDATE%" == "0" GOTO :CALL_GCLIENT
 :: Synchronize the root directory before deferring control back to gclient.py.
 call "%~dp0update_depot_tools.bat" %*
 :: Abort the script if we failed to update depot_tools.
-IF %errorlevel% NEQ 0 (
+IF %ERRORLEVEL% NEQ 0 (
-  goto :EOF
+  exit /b %ERRORLEVEL%
 )
 
 :CALL_GCLIENT

gsutil.py.bat

@@ -10,8 +10,8 @@ IF "%DEPOT_TOOLS_UPDATE%" == "0" GOTO :CALL_GSUTIL
 :: Synchronize the root directory before deferring control back to gsutil.py.
 call "%~dp0update_depot_tools.bat" %*
 :: Abort the script if we failed to update depot_tools.
-IF %errorlevel% NEQ 0 (
+IF %ERRORLEVEL% NEQ 0 (
-  goto :EOF
+  exit /b %ERRORLEVEL%
 )
 
 :CALL_GSUTIL

update_depot_tools

@@ -129,7 +129,11 @@ if [ "X$DEPOT_TOOLS_UPDATE" != "X0" ]; then
   if [ -e "$base_dir/.git" ]; then
     cd "$base_dir"
     update_git_repo
+    UPDATE_RESULT=$?
     cd - > /dev/null
+    if [[ $UPDATE_RESULT -ne 0 ]]; then
+      exit $UPDATE_RESULT
+    fi
   fi
 
   # Sync CIPD-boostrapped packages.

update_depot_tools.bat

@@ -5,17 +5,24 @@
 
 :: This batch file will try to sync the root directory.
 
-setlocal
+setlocal enabledelayedexpansion
 
 :: Windows freaks out if a file is overwritten while it's being executed.  Copy
 :: this script off to a temporary location and reinvoke from there before
 :: running any git commands.
 IF "%~nx0"=="update_depot_tools.bat" (
   COPY /Y "%~dp0update_depot_tools.bat" "%TEMP%\update_depot_tools_tmp.bat" >nul
-  if errorlevel 1 goto :EOF
+  if errorlevel 1 (
+    echo Error updating depot_tools, can't copy update_depot_tools.bat to TEMP.
+    :: !VAR! syntax is used to get delayed expansion, because %VAR% syntax would
+    :: return a value that was set prior entering the IF () block.
+    exit /b !ERRORLEVEL!
+  )
   :: Use call/exit to avoid leaving an orphaned window title.
   call "%TEMP%\update_depot_tools_tmp.bat" "%~dp0" %*
-  exit /b %ERRORLEVEL%
+  :: !VAR! syntax is used to get delayed expansion, because %VAR% syntax would
+  :: return a value that was set prior entering the IF () block.
+  exit /b !ERRORLEVEL!
 )
 
 set DEPOT_TOOLS_DIR=%~1
@@ -25,15 +32,16 @@ SHIFT
 IF EXIST "%DEPOT_TOOLS_DIR%.disable_auto_update" GOTO :EOF
 IF "%DEPOT_TOOLS_UPDATE%" == "0" GOTO :EOF
 
+echo Updating depot_tools...
 set GIT_URL=https://chromium.googlesource.com/chromium/tools/depot_tools.git
 
 :: Download git for the first time if it's not present.
 call git --version > nul 2>&1
-if %errorlevel% == 0 goto :GIT_UPDATE
+if %ERRORLEVEL% == 0 goto :GIT_UPDATE
 call "%DEPOT_TOOLS_DIR%bootstrap\win_tools.bat"
 if errorlevel 1 (
   echo Error updating depot_tools, no revision tool found.
-  goto :EOF
+  exit /b %ERRORLEVEL%
 )
 
 :GIT_UPDATE
@@ -60,7 +68,7 @@ call git fetch -q origin > NUL
 call git checkout -q origin/main > NUL
 if errorlevel 1 (
   echo Failed to update depot_tools.
-  goto :EOF
+  exit /b %ERRORLEVEL%
 )
 
 :: Sync CIPD and CIPD client tools.