[do-not-upstream][semihost] Revert "semihost: ARM semihosting 'open' doesn't support stdin"

This reverts commit [81e6fa2](picolibc@81e6fa2)
As This commit introduced a workaround specifically for ARM that is no longer necessary or desirable.

Signed-off-by: Mostafa Salman <[email protected]>

Author: mostafa-salmaan

semihost/mapstdio.c

@@ -42,20 +42,21 @@
 #include <errno.h>
 #include <stdbool.h>
 
-static int fd_stdout, fd_stderr;
+static int fd_stdin, fd_stdout, fd_stderr;
 static bool _check_done;
 
 int
 _map_stdio(int fd)
 {
 	if (!_check_done) {
 		_check_done = true;
+		fd_stdin  = sys_semihost_open(":tt", 0);
 		fd_stdout = sys_semihost_open(":tt", 4);
 		fd_stderr = sys_semihost_open(":tt", 8);
 	}
 	switch (fd) {
         case 0:
-                return -1;
+                return fd_stdin;
 	case 1:
 		return fd_stdout;
 	case 2:

semihost/read.c

@@ -44,11 +44,6 @@
 ssize_t
 read(int fd, void *buf, size_t count)
 {
-        if (fd == 0) {
-                int ch = sys_semihost_getc((FILE *) 0);
-                *(char *) buf = ch;
-                return 1;
-        }
 	fd = _map_stdio(fd);
 	uintptr_t ret = sys_semihost_read(fd, buf, count);