[libxml2] Increase warning level to /W3 under MSVC

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 25499fc2295d0a2844b6b1fb356ce4c46363216b
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Mon Oct 9 02:39:16 2017 +0200

    Increase warning level to /W3 under MSVC
    
    With the exception of timsort.h and warnings 4244 and 4267, the MSVC
    build is now warnings-free with /W3.

 win32/Makefile.msvc |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/win32/Makefile.msvc b/win32/Makefile.msvc
index bb7fa4a..115a451 100644
--- a/win32/Makefile.msvc
+++ b/win32/Makefile.msvc
@@ -43,7 +43,7 @@ CPPFLAGS = $(CPPFLAGS) /D "_REENTRANT"
 
 # The compiler and its options.
 CC = cl.exe
-CFLAGS = /nologo /D "_WINDOWS" /D "_MBCS" /D "NOLIBTOOL" /W1 $(CRUNTIME)
+CFLAGS = /nologo /D "_WINDOWS" /D "_MBCS" /D "NOLIBTOOL" /W3 /wd4244 /wd4267 $(CRUNTIME)
 CFLAGS = $(CFLAGS) /I$(XML_SRCDIR) /I$(XML_SRCDIR)\include /I$(INCPREFIX)
 !if "$(WITH_THREADS)" != "no"
 CFLAGS = $(CFLAGS) /D "_REENTRANT"