Fix: allow to override lapack/blas versions

com.oracle.truffle.r.native/gnur/Makefile.libs

@@ -31,8 +31,18 @@ $(error no platform.mk available)
 endif
 endif
 
+# blas and lapack implementations can be overridden using the following environment variables
+BLAS_LAPACK_DIR ?= $(GNUR_HOME_BINARY)/lib
+BLAS_SOURCE ?= $(BLAS_LAPACK_DIR)/libRblas$(DYLIB_EXT)
+LAPACK_SOURCE ?= $(BLAS_LAPACK_DIR)/libRlapack$(DYLIB_EXT)
+
+$(info BLAS_LAPACK_DIR : $(BLAS_LAPACK_DIR))
+$(info BLAS_SOURCE : $(BLAS_SOURCE))
+$(info LAPACK_SOURCE : $(LAPACK_SOURCE))
+
 BLAS_TARGET := $(FASTR_LIB_DIR)/libRblas$(DYLIB_EXT)
 LAPACK_TARGET := $(FASTR_LIB_DIR)/libRlapack$(DYLIB_EXT)
+
 # at a minimum we need to know where libpcre/libz/libgfortran/libquadmath are located,
 # to keep the Java side simpler, we (may) copy them to $(FASTR_LIB_DIR) unless
 # they were found in the standard system locations
@@ -47,10 +57,10 @@ $(FASTR_LIB_DIR):
 	mkdir -p $(FASTR_LIB_DIR)
 
 $(BLAS_TARGET): $(GNUR_HOME_BINARY)/lib/libRblas$(DYLIB_EXT)
-	cp $(GNUR_HOME_BINARY)/lib/libRblas$(DYLIB_EXT) $(BLAS_TARGET)
+	cp $(BLAS_SOURCE) $(BLAS_TARGET)
 
 $(LAPACK_TARGET): $(GNUR_HOME_BINARY)/lib/libRlapack$(DYLIB_EXT)
-	cp $(GNUR_HOME_BINARY)/lib/libRlapack$(DYLIB_EXT) $(LAPACK_TARGET)
+	cp $(LAPACK_SOURCE) $(LAPACK_TARGET)
 ifeq ($(OS_NAME),Darwin)
 # libRblas depends on libgfortran, libquadmath
 # libRlapack depends on libgfortran, libquadmath, libRblas, libR