RISC-V: Add gdb sim and newlib nano support. Fix a few misc minor bugs.

libgloss/riscv/sys_sbrk.c

@@ -1,3 +1,31 @@
+#ifdef USING_SIM_SPECS
+
+// Gdb simulator requires that sbrk be implemented without a syscall.
+extern char _end[];                /* _end is set in the linker command file */
+char *heap_ptr;
+
+/*
+ * sbrk -- changes heap size size. Get nbytes more
+ *         RAM. We just increment a pointer in what's
+ *         left of memory on the board.
+ */
+char *
+_sbrk (nbytes)
+     int nbytes;
+{
+  char        *base;
+
+  if (!heap_ptr)
+    heap_ptr = (char *)&_end;
+  base = heap_ptr;
+  heap_ptr += nbytes;
+
+  return base;
+}
+
+#else
+
+// QEMU uses a syscall.
 #include <machine/syscall.h>
 #include <sys/types.h>
 #include "internal_syscall.h"
@@ -25,3 +53,4 @@ _sbrk(ptrdiff_t incr)
   heap_end += incr;
   return (void *)(heap_end - incr);
 }
+#endif