Fixes for RISC V build (#321)

* Fixes for RISCV build

* Consolidate compiler flags

tensorflow/lite/micro/tools/make/targets/mcu_riscv_makefile.inc

 # Settings for RISCV 32-bit MCU toolchain.
-ifeq ($(TARGET), riscv32_mcu)
-  TARGET_ARCH := riscv32_mcu
-  TARGET_TOOLCHAIN_PREFIX := riscv64-unknown-elf-
-
-  $(eval $(call add_third_party_download,$(RISCV_TOOLCHAIN_URL),$(RISCV_TOOLCHAIN_MD5),riscv_toolchain,))
-  $(eval $(call add_third_party_download,$(SIFIVE_FE310_LIB_URL),$(SIFIVE_FE310_LIB_MD5),sifive_fe310_lib,))
-
-  PLATFORM_FLAGS = \
-    -march=rv32imac \
-    -mabi=ilp32 \
-    -mcmodel=medany \
-    -mexplicit-relocs \
-    -fno-builtin-printf \
-    -fno-exceptions \
-    -DTF_LITE_MCU_DEBUG_LOG \
-    -DTF_LITE_USE_GLOBAL_CMATH_FUNCTIONS \
-    -fno-unwind-tables \
-    -ffunction-sections \
-    -fdata-sections \
-    -funsigned-char \
-    -Wvla \
-    -Wall \
-    -Wextra \
-    -Wsign-compare \
-    -Wdouble-promotion \
-    -Wshadow \
-    -Wunused-variable \
-    -Wmissing-field-initializers \
-    -Wno-unused-parameter \
-    -Wno-write-strings \
-    -Wunused-function \
-    -fno-delete-null-pointer-checks \
-    -fno-threadsafe-statics \
-    -fomit-frame-pointer \
-    -fno-use-cxa-atexit \
-    -Os
-
-  CXXFLAGS += $(PLATFORM_FLAGS) \
-    -fpermissive \
-    -fno-rtti \
-    --std=gnu++11
-
-  CCFLAGS += $(PLATFORM_FLAGS)
-
-  BUILD_TYPE := micro
-
-  INCLUDES += \
-    -I$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/include \
-    -I$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/drivers/ \
-    -I$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/env \
-    -I$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/env/freedom-e300-hifive1
-
-  MICROLITE_CC_SRCS += \
-    $(wildcard tensorflow/lite/micro/riscv32_mcu/*.cc)
-
-  LDFLAGS += \
-   -T$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/env/freedom-e300-hifive1/flash.lds \
-   -nostartfiles \
-   -L$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/env \
-   --specs=nano.specs
+TARGET_ARCH := riscv32_mcu
+TARGET_TOOLCHAIN_PREFIX := riscv64-unknown-elf-
+
+export PATH := $(MAKEFILE_DIR)/downloads/riscv_toolchain/bin/:$(PATH)
+
+$(eval $(call add_third_party_download,$(RISCV_TOOLCHAIN_URL),$(RISCV_TOOLCHAIN_MD5),riscv_toolchain,))
+$(eval $(call add_third_party_download,$(SIFIVE_FE310_LIB_URL),$(SIFIVE_FE310_LIB_MD5),sifive_fe310_lib,))
+
+PLATFORM_FLAGS = \
+  -march=rv32imac \
+  -mabi=ilp32 \
+  -mcmodel=medany \
+  -mexplicit-relocs \
+  -fno-builtin-printf \
+  -fno-exceptions \
+  -DTF_LITE_MCU_DEBUG_LOG \
+  -DTF_LITE_USE_GLOBAL_CMATH_FUNCTIONS \
+  -funsigned-char \
+  -fno-delete-null-pointer-checks \
+  -fomit-frame-pointer
+
+CXXFLAGS += $(PLATFORM_FLAGS) \
+  -fpermissive \
+  -fno-rtti \
+  -fno-threadsafe-statics \
+  -fno-use-cxa-atexit \
+  -DTF_LITE_USE_GLOBAL_MIN \
+  -DTF_LITE_USE_GLOBAL_MAX \
+  --std=gnu++11
+
+CCFLAGS += $(PLATFORM_FLAGS)
+
+BUILD_TYPE := micro
+
+INCLUDES += \
+  -I$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/include \
+  -I$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/drivers/ \
+  -I$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/env \
+  -I$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/env/freedom-e300-hifive1
+
+MICROLITE_CC_SRCS += \
+  $(wildcard tensorflow/lite/micro/riscv32_mcu/*.cc)
+
+LDFLAGS += \
+ -T$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/env/freedom-e300-hifive1/flash.lds \
+ -L$(MAKEFILE_DIR)/downloads/sifive_fe310_lib/bsp/env \
+ --specs=nano.specs
 
 # These are microcontroller-specific rules for converting the ELF output
 # of the linker into a binary image that can be loaded directly.
-  OBJCOPY := $(TARGET_TOOLCHAIN_PREFIX)objcopy
-  $(BINDIR)/%.bin: $(BINDIR)/%
-		@mkdir -p $(dir $@)
-		$(OBJCOPY) $< $@ -O binary
-endif
+OBJCOPY := $(TARGET_TOOLCHAIN_PREFIX)objcopy
+$(BINDIR)/%.bin: $(BINDIR)/%
+	@mkdir -p $(dir $@)
+	$(OBJCOPY) $< $@ -O binary