Use xtensa-lx106-elf-ar instead of native ar.

See https://github.com/pfalcon/esp-open-sdk/issues/132

Makefile

@@ -166,19 +166,19 @@ sdk_patch: .sdk_patch_$(VENDOR_SDK)
 .sdk_patch_1.5.2:
 	echo -e "#undef ESP_SDK_VERSION\n#define ESP_SDK_VERSION 010502" >>$(VENDOR_SDK_DIR)/include/esp_sdk_ver.h
 	$(PATCH) -d $(VENDOR_SDK_DIR) -p1 < c_types-c99.patch
-	cd $(VENDOR_SDK_DIR)/lib; mkdir -p tmp; cd tmp; ar x ../libcrypto.a; cd ..; ar rs libwpa.a tmp/*.o
+	cd $(VENDOR_SDK_DIR)/lib; mkdir -p tmp; cd tmp; $(TOOLCHAIN)/bin/xtensa-lx106-elf-ar x ../libcrypto.a; cd ..; $(TOOLCHAIN)/bin/xtensa-lx106-elf-ar rs libwpa.a tmp/*.o
 	@touch $@
 
 .sdk_patch_1.5.1:
 	echo -e "#undef ESP_SDK_VERSION\n#define ESP_SDK_VERSION 010501" >>$(VENDOR_SDK_DIR)/include/esp_sdk_ver.h
 	$(PATCH) -d $(VENDOR_SDK_DIR) -p1 < c_types-c99.patch
-	cd $(VENDOR_SDK_DIR)/lib; mkdir -p tmp; cd tmp; ar x ../libcrypto.a; cd ..; ar rs libwpa.a tmp/*.o
+	cd $(VENDOR_SDK_DIR)/lib; mkdir -p tmp; cd tmp; $(TOOLCHAIN)/bin/xtensa-lx106-elf-ar x ../libcrypto.a; cd ..; $(TOOLCHAIN)/bin/xtensa-lx106-elf-ar rs libwpa.a tmp/*.o
 	@touch $@
 
 .sdk_patch_1.5.0:
 	echo -e "#undef ESP_SDK_VERSION\n#define ESP_SDK_VERSION 010500" >>$(VENDOR_SDK_DIR)/include/esp_sdk_ver.h
 	$(PATCH) -d $(VENDOR_SDK_DIR) -p1 < c_types-c99.patch
-	cd $(VENDOR_SDK_DIR)/lib; mkdir -p tmp; cd tmp; ar x ../libcrypto.a; cd ..; ar rs libwpa.a tmp/*.o
+	cd $(VENDOR_SDK_DIR)/lib; mkdir -p tmp; cd tmp; $(TOOLCHAIN)/bin/xtensa-lx106-elf-ar x ../libcrypto.a; cd ..; $(TOOLCHAIN)/bin/xtensa-lx106-elf-ar rs libwpa.a tmp/*.o
 	@touch $@
 
 .sdk_patch_1.4.0: