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.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>

Author: peff

Makefile

@@ -1268,6 +1268,7 @@ 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)),)