fix signedness of N_ARENA

Fixes
CFLAGS=-Wformat-signedness make CC=gcc CONFIG_STATS=true
build failure

Author: rdevshp

Android.bp

@@ -25,7 +25,7 @@ common_cflags = [
     "-DREGION_QUARANTINE_SKIP_THRESHOLD=33554432", // 32MiB
     "-DFREE_SLABS_QUARANTINE_RANDOM_LENGTH=32",
     "-DCONFIG_CLASS_REGION_SIZE=34359738368", // 32GiB
-    "-DN_ARENA=1",
+    "-DN_ARENA=1U",
     "-DCONFIG_STATS=true",
     "-DCONFIG_SELF_INIT=false",
 ]

Makefile

@@ -112,7 +112,7 @@ CPPFLAGS += \
     -DREGION_QUARANTINE_SKIP_THRESHOLD=$(CONFIG_REGION_QUARANTINE_SKIP_THRESHOLD) \
     -DFREE_SLABS_QUARANTINE_RANDOM_LENGTH=$(CONFIG_FREE_SLABS_QUARANTINE_RANDOM_LENGTH) \
     -DCONFIG_CLASS_REGION_SIZE=$(CONFIG_CLASS_REGION_SIZE) \
-    -DN_ARENA=$(CONFIG_N_ARENA) \
+    -DN_ARENA=$(CONFIG_N_ARENA)U \
     -DCONFIG_STATS=$(CONFIG_STATS) \
     -DCONFIG_SELF_INIT=$(CONFIG_SELF_INIT) \
     -DCONFIG_LABEL_MEMORY=$(CONFIG_LABEL_MEMORY)

README.md

@@ -228,7 +228,7 @@ the size of the empty slab caches and quarantines, saving a lot of memory,
 since those are currently based on the size of the largest size class):
 
     make \
-    N_ARENA=1 \
+    N_ARENA=1U \
     CONFIG_EXTENDED_SIZE_CLASSES=false
 
 The following boolean configuration options are available: