Add FreeRTOS heap4 intro card

crt0.S

@@ -0,0 +1,33 @@
+  .text
+  .global _start
+  .type   _start, @function
+
+_start:
+  # Initialize global pointer.
+.option push
+.option norelax
+  la      gp, __global_pointer$
+.option pop
+
+  # Stack pointer is intentionally not set here.
+  # In the Hazard3 testbench flow, common/init.S enters _start with sp
+  # already loaded from __stack_top and adjusted to leave the argc/argv
+  # area expected by newlib-style startup code.
+
+  # Clear the .bss segment so debug globals start in a known state.
+  la      a0, __bss_start
+  la      a1, __bss_end
+
+clear_bss:
+  bgeu    a0, a1, finish_bss
+  sb      x0, 0(a0)
+  addi    a0, a0, 1
+  j       clear_bss
+finish_bss:
+
+  call    main
+
+  # Exit the testbench with main() return code (Hazard3 init.S provides _exit).
+  tail    _exit
+
+  .size  _start, .-_start