It works with GCC!

barebones/Makefile

@@ -7,8 +7,9 @@ PREFIX:=riscv64-unknown-elf
 GPIO_Toggle:=EXAM/GPIO/GPIO_Toggle/User
 
 CFLAGS:= \
-	-Os -flto -ffunction-sections \
-	-march=rv32emc \
+	-g -Os -flto -ffunction-sections \
+	-static-libgcc -lgcc \
+	-march=rv32ec \
 	-mabi=ilp32e \
 	-I/usr/include/newlib \
 	-nostdlib \

official/Makefile

@@ -7,8 +7,9 @@ PREFIX:=riscv64-unknown-elf
 GPIO_Toggle:=EXAM/GPIO/GPIO_Toggle/User
 
 CFLAGS:= \
-	-Os -flto -ffunction-sections \
-	-march=rv32emc \
+	-g -Os -flto -ffunction-sections \
+	-static-libgcc -lgcc \
+	-march=rv32ec \
 	-mabi=ilp32e \
 	-I/usr/include/newlib \
 	-nostdlib \

official/embedlibc.c

@@ -4,6 +4,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdarg.h>
+#include <limits.h>
 
 int errno;
 int _write(int fd, const char *buf, int size);
@@ -25,6 +26,7 @@ int printf(const char* format, ...)
 	return ret_status;
 }
 
+
 /* Some stuff from MUSL