[PATCH v2 1/6] mingw: stop using nedmalloc

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

The vendored nedmalloc allocator under compat/nedmalloc/ has been
unmaintained upstream for a very long time: the original repository at
https://github.com/ned14/nedmalloc received its last commit on July 5,
2014, and was archived (made read-only) by its owner on March 15, 2019.
Our copy has been carried forward unchanged ever since.

The Git for Windows commit that introduced mimalloc as a replacement
on Windows ("mingw: use mimalloc", 2019-06-24, present in the Git for
Windows branch thicket but not upstream) already observed at that time
that nedmalloc had ceased to see any updates for several years.

This came to a head when the Git for Windows SDK upgraded to GCC 16:
the `add_segment()` function in `compat/nedmalloc/malloc.c.h` declares
`int nfences = 0` and only references it inside an `assert()`, which
GCC 16 now flags as `-Wunused-but-set-variable`. Combined with the
`-Werror` enabled by `DEVELOPER=1`, this turns into a hard build
failure:

	compat/nedmalloc/malloc.c.h: In function 'add_segment':
	compat/nedmalloc/malloc.c.h:3897:7: error: variable 'nfences' set but not used [-Werror=unused-but-set-variable=]
	 3897 |   int nfences = 0;
	      |       ^~~~~~~
	cc1.exe: all warnings being treated as errors

The same source built without complaint under GCC 15.2.0; the
regression was bisected to the SDK package update at
https://github.com/git-for-windows/git-sdk-64/commit/188d93dd455
(`mingw-w64-x86_64-gcc 15.2.0-14 -> 16.1.0-1`), with the failing CI
run captured at
https://github.com/git-for-windows/git-sdk-64/actions/runs/25244795074.

Rather than patch the unmaintained vendored sources to silence the
warning, stop opting into nedmalloc altogether on Windows. The
platform allocator is what every non-MINGW build already uses, and a
fresh build of git.git's master against a minimal Git for Windows SDK
upgraded to GCC 16 completes successfully.

The compat/nedmalloc/ subtree itself is removed by subsequent commits
in this series.

Assisted-by: Opus 4.7
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 config.mak.uname                    | 3 ---
 contrib/buildsystems/CMakeLists.txt | 3 +--
 meson.build                         | 1 -
 3 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/config.mak.uname b/config.mak.uname
index 5feb582558..3636b98238 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -758,9 +758,6 @@ ifeq ($(uname_S),MINGW)
 	HAVE_LIBCHARSET_H = YesPlease
 	USE_GETTEXT_SCHEME = fallthrough
 	USE_LIBPCRE = YesPlease
-        ifneq (CLANGARM64,$(MSYSTEM))
-		USE_NED_ALLOCATOR = YesPlease
-        endif
         ifeq (/mingw64,$(subst 32,64,$(subst clangarm,mingw,$(prefix))))
 		# Move system config into top-level /etc/
 		ETC_GITCONFIG = ../etc/gitconfig
diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index 81b4306e72..9d6b98ecb6 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -255,7 +255,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
 	add_compile_definitions(HAVE_ALLOCA_H NO_POSIX_GOODIES NATIVE_CRLF NO_UNIX_SOCKETS WIN32
 				_CONSOLE DETECT_MSYS_TTY STRIP_EXTENSION=".exe"  NO_SYMLINK_HEAD UNRELIABLE_FSTAT
 				NOGDI OBJECT_CREATION_MODE=1 __USE_MINGW_ANSI_STDIO=0
-				USE_NED_ALLOCATOR OVERRIDE_STRDUP MMAP_PREVENTS_DELETE USE_WIN32_MMAP
+				OVERRIDE_STRDUP MMAP_PREVENTS_DELETE USE_WIN32_MMAP
 				HAVE_WPGMPTR ENSURE_MSYSTEM_IS_SET HAVE_RTLGENRANDOM)
 	list(APPEND compat_SOURCES
 		compat/mingw.c
@@ -267,7 +267,6 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
 		compat/win32/syslog.c
 		compat/win32/trace2_win32_process_info.c
 		compat/win32/dirent.c
-		compat/nedmalloc/nedmalloc.c
 		compat/strdup.c)
 	set(NO_UNIX_SOCKETS 1)
 
diff --git a/meson.build b/meson.build
index 11488623bf..e896bc15a1 100644
--- a/meson.build
+++ b/meson.build
@@ -1285,7 +1285,6 @@ elif host_machine.system() == 'windows'
     'compat/win32/pthread.c',
     'compat/win32/syslog.c',
     'compat/win32mmap.c',
-    'compat/nedmalloc/nedmalloc.c',
   ]
 
   libgit_c_args += [
-- 
gitgitgadget