build system: use riscv-none-elf as triplet

Use riscv-none-elf instead of legacy riscv-none-embed as target triplet for
RISC-V development. However, if ricsv-none-elf is not present but
riscv-none-embed is, fall back to legacy triplet (and print an info message
about this behavior).

dist/tools/ci/print_toolchain_versions.sh

@@ -126,6 +126,7 @@ for p in \
          arm-none-eabi \
          avr mips-mti-elf \
          msp430-elf \
+         riscv-none-elf \
          riscv-none-embed \
          xtensa-esp32-elf \
          xtensa-esp8266-elf \
@@ -141,6 +142,7 @@ for p in \
          arm-none-eabi \
          mips-mti-elf \
          msp430-elf \
+         riscv-none-elf \
          riscv-none-embed \
          xtensa-esp32-elf \
          xtensa-esp8266-elf \

makefiles/arch/riscv.inc.mk

@@ -1,5 +1,16 @@
 # Target architecture for the build.
-TARGET_ARCH ?= riscv-none-embed
+TARGET_ARCH ?= riscv-none-elf
+
+# If TARGET_ARCH wasn't set by user, fall back to legacy riscv-none-embed
+# triplet if ricsv-none-elf is missing but riscv-none-embed is present
+ifeq (riscv-none-elf,$(TARGET_ARCH))
+  ifeq (,$(shell which $(TARGET_ARCH)-gcc))
+    ifneq (,$(shell which riscv-none-embed-gcc))
+      $(info Falling back to legacy riscv-none-embed toolchain)
+      TARGET_ARCH := riscv-none-embed
+    endif
+  endif
+endif
 
 # define build specific options
 CFLAGS_CPU   = -march=rv32imac -mabi=ilp32 -mcmodel=medlow -msmall-data-limit=8