Fix _echo to be uniform (_echo just needs to be defined for it to be on). (dotnet#12475)

Author: vancem

build.cmd

@@ -1,4 +1,4 @@
-@if "%_echo%" neq "on" echo off
+@if not defined _echo @echo off
 setlocal
 
 if /I [%1] == [-?] goto Usage
@@ -23,4 +23,4 @@ echo For more information: "https://github.com/dotnet/corefx/blob/master/Documen
 echo ----------------------------------------------------------------------------
 echo.
 echo.
-goto :Build
+goto :Build

clean.cmd

@@ -1,4 +1,4 @@
-@if "%_echo%" neq "on" echo off
+@if not defined _echo @echo off
 setlocal EnableDelayedExpansion
 
 echo Stop VBCSCompiler.exe execution.
@@ -31,4 +31,4 @@ echo     -all   - Combines all of the above.
 echo.
 echo If no option is specified then clean.cmd -b is implied.
 
-exit /b 1
+exit /b 1

init-tools.cmd

@@ -1,4 +1,4 @@
-@if "%_echo%" neq "on" echo off
+@if not defined _echo @echo off
 setlocal
 
 set INIT_TOOLS_LOG=%~dp0init-tools.log
@@ -80,4 +80,4 @@ if %UPDATE_CLI_ERRORLEVEL% GTR 1 (
 :: Create sempahore file
 echo Done initializing tools.
 echo Init-Tools.cmd completed for BuildTools Version: %BUILDTOOLS_VERSION% > "%BUILD_TOOLS_SEMAPHORE%"
-exit /b 0
+exit /b 0

run-test.cmd

@@ -1,4 +1,4 @@
-@if "%_echo%" neq "on" echo off
+@if not defined _echo @echo off
 
 :: To run tests outside of MSBuild.exe
 :: %1 is the path to the tests\<OSConfig> folder

run.cmd

@@ -1,4 +1,4 @@
-@if "%_echo%" neq "on" echo off
+@if not defined _echo @echo off
 setlocal
 
 if not defined VisualStudioVersion (
@@ -24,4 +24,4 @@ set _toolRuntime=%~dp0Tools
 set _dotnet=%_toolRuntime%\dotnetcli\dotnet.exe
 
 call %_dotnet% %_toolRuntime%\run.exe %*
-exit /b %ERRORLEVEL%
+exit /b %ERRORLEVEL%

src/Native/build-native.cmd

@@ -1,4 +1,4 @@
-@if "%_echo%" neq "on" echo off
+@if not defined _echo @echo off
 setlocal
 
 :SetupArgs