Adding way to specify a custom RCCL shared library file to link against

src/Makefile

@@ -14,13 +14,14 @@ DEBUG ?= 0
 HIPCC = $(ROCM_HOME)/hip/bin/hipcc
 CXX = $(HIPCC)
 
+
 HIPCUFLAGS :=
 HIPCUFLAGS += -I$(ROCM_HOME)/include
 HIPCUFLAGS += -I$(ROCM_HOME)/include/rccl
 HIPCUFLAGS += -I$(ROCM_HOME)/hip/include/hip
 HIPCUFLAGS += -I$(ROCM_HOME)/hiprand/include
 LDFLAGS    := -L$(ROCM_HOME)/lib -lhsa-runtime64 -lrt
-HIPLDFLAGS := -L$(ROCM_HOME)/lib -lhsa-runtime64 -lrt
+HIPLDFLAGS := $(CUSTOM_RCCL_LIB) -L$(ROCM_HOME)/lib -lhsa-runtime64 -lrt
 
 ifeq ($(DEBUG), 0)
 HIPCUFLAGS += -O3