Allow to supply custom blas/lapack libraries

Author: steve-s

com.oracle.truffle.r.native/fficall/Makefile

@@ -64,10 +64,6 @@ ifeq ($(OS_NAME), Darwin)
 VERSION_FLAGS := -current_version $(R_VERSION) -compatibility_version $(R_VERSION)
 endif
 
-# TODO: can we remove those?
-BLAS_TARGET := $(FASTR_LIB_DIR)/libRblas$(DYLIB_EXT)
-LAPACK_TARGET := $(FASTR_LIB_DIR)/libRlapack$(DYLIB_EXT)
-
 all: $(R_LIB)
 
 # use sentinels to avoid (usually unnecessary) rebuilds.

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

@@ -31,8 +31,14 @@ $(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)
+
 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 +53,10 @@ $(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