radix tree test suite: Build 32 bit binaries

Add option 'make BUILD=32' for building 32-bit binaries.
Signed-off-by: NRehas Sachdeva <aquannie@gmail.com>
Signed-off-by: NMatthew Wilcox <mawilcox@microsoft.com>

tools/testing/radix-tree/Makefile

@@ -10,6 +10,10 @@ ifndef SHIFT
 	SHIFT=3
 endif
 
+ifeq ($(BUILD), 32)
+	CFLAGS += -m32
+endif
+
 targets: mapshift $(TARGETS)
 
 main:	$(OFILES)