mingw: use mimalloc

Thorough benchmarking with repacking a subset of linux.git (the commit
history reachable from 93a6fef ([PATCH] fix the SYSCTL=n compilation,
2007-02-28), to be precise) suggest that this allocator is on par, in
multi-threaded situations maybe even better than nedmalloc:

`git repack -adfq` with mimalloc, 8 threads:

31.166991900 27.576763800 28.712311000 27.373859000 27.163141900

`git repack -adfq` with nedmalloc, 8 threads:

31.915032900 27.149883100 28.244933700 27.240188800 28.580849500

While these measurements were not executed with complete scientific
rigor, as no hardware was dedicated to this benchmarking, it shows that
mimalloc and nedmalloc perform almost the same, nedmalloc with a bit
higher variance and also slightly higher average (further testing
suggests that nedmalloc performs worse in multi-threaded situations than
in single-threaded ones).

In short: mimalloc seems to be slightly better suited for our purposes
than nedmalloc.

Seeing that mimalloc is developed actively, while nedmalloc ceased to
see any updates already years ago, let's use mimalloc on Windows
instead.

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

Author: dscho

config.mak.uname

@@ -656,7 +656,7 @@ ifeq ($(uname_S),MINGW)
 	USE_WIN32_IPC = YesPlease
 	USE_WIN32_MMAP = YesPlease
 	MMAP_PREVENTS_DELETE = UnfortunatelyYes
-	USE_NED_ALLOCATOR = YesPlease
+	USE_MIMALLOC = YesPlease
 	UNRELIABLE_FSTAT = UnfortunatelyYes
 	OBJECT_CREATION_USES_RENAMES = UnfortunatelyNeedsTo
 	NO_REGEX = YesPlease
@@ -724,7 +724,6 @@ else
 		HAVE_LIBCHARSET_H = YesPlease
 		USE_GETTEXT_SCHEME = fallthrough
 		USE_LIBPCRE = YesPlease
-		USE_NED_ALLOCATOR = YesPlease
 		NO_PYTHON =
 		ifeq (/mingw64,$(subst 32,64,$(prefix)))
 			# Move system config into top-level /etc/