Makefile: force -O0 when compiling with SANITIZE=leak

Cherry pick commit d3775de (Makefile: force -O0 when compiling with
SANITIZE=leak, 2022-10-18), as otherwise the leak checker at GitHub
Actions CI seems to fail with a false positive.

[Backported to v2.37.0 for easier merging e.g. into Git for Windows]

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: peff

Makefile

@@ -1323,6 +1323,7 @@ BASIC_CFLAGS += -DSHA1DC_FORCE_ALIGNED_ACCESS
 endif
 ifneq ($(filter leak,$(SANITIZERS)),)
 BASIC_CFLAGS += -DSUPPRESS_ANNOTATED_LEAKS
+BASIC_CFLAGS += -O0
 SANITIZE_LEAK = YesCompiledWithIt
 endif
 ifneq ($(filter address,$(SANITIZERS)),)