mingw: do not use nedmalloc on Windows/ARM64

It does not compile there, and seeing as nedmalloc has been pretty much
unmaintained since at least November 2017, as per
ned14/nedmalloc#20 (comment),
there is also no hope that any fixes will materialize there.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

config.mak.uname

@@ -742,7 +742,9 @@ ifeq ($(uname_S),MINGW)
 	HAVE_LIBCHARSET_H = YesPlease
 	USE_GETTEXT_SCHEME = fallthrough
 	USE_LIBPCRE = YesPlease
-	USE_NED_ALLOCATOR = YesPlease
+	ifneq (CLANGARM64,$(MSYSTEM))
+		USE_NED_ALLOCATOR = YesPlease
+	endif
         ifeq (/mingw64,$(subst 32,64,$(prefix)))
 		# Move system config into top-level /etc/
 		ETC_GITCONFIG = ../etc/gitconfig