don't error on warnings with clang

Author: henderkes

.github/scripts/windows/build_task.bat

@@ -31,7 +31,11 @@ rem C4018: comparison: signed/unsigned mismatch
 rem C4146: unary minus operator applied to unsigned type
 rem C4244: type conversion, possible loss of data
 rem C4267: 'size_t' type conversion, possible loss of data
-set CFLAGS=/W3 /WX /wd4018 /wd4146 /wd4244 /wd4267
+if "%CLANG_TOOLSET%" equ "1" (
+	set CFLAGS=/W3 /wd4018 /wd4146 /wd4244 /wd4267
+) else (
+	set CFLAGS=/W3 /WX /wd4018 /wd4146 /wd4244 /wd4267
+)
 
 cmd /c configure.bat ^
 	--enable-snapshot-build ^