Elevate Windows CI to /W3 (sans C4018/C4267) (GH-17665)

C4018[1] is about unsigned/signed comparisons; C4267[2] is about
conversion from `size_t` to a "smaller" type.  We likely should resolve
these warnings in the long run, but for now, it seems like a no brainer
to elevate to `/W3` even if we have to exempt two additional categories
of warnings, since we can catch some others.  And we no longer need to
elevate C4010[3] to a higher level to catch it.

[1] <https://learn.microsoft.com/en-us/cpp/error-messages/compiler-warnings/compiler-warning-level-3-c4018>
[2] <https://learn.microsoft.com/en-us/cpp/error-messages/compiler-warnings/compiler-warning-level-3-c4267>
[3] <https://learn.microsoft.com/de-de/cpp/error-messages/compiler-warnings/compiler-warning-level-3-c4013>

Author: cmb69

.github/scripts/windows/build_task.bat

@@ -32,7 +32,11 @@ if "%THREAD_SAFE%" equ "0" set ADD_CONF=%ADD_CONF% --disable-zts
 if "%INTRINSICS%" neq "" set ADD_CONF=%ADD_CONF% --enable-native-intrinsics=%INTRINSICS%
 if "%ASAN%" equ "1" set ADD_CONF=%ADD_CONF% --enable-sanitizer --enable-debug-pack
 
-set CFLAGS=/W2 /WX /w14013 /wd4146 /wd4244
+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
 
 cmd /c configure.bat ^
 	--enable-snapshot-build ^