fix(libc): remove __putchar alias

This issue was triggered by sparse tool:
lib/libc/putchar.c:9:5: warning:
 symbol '__putchar' was not declared. Should it be static?
Instead of setting __putchar as static, just remove the function and
directly use putchar() with a weak attribute.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: Ib35e4ba064f06010851bb860269b08462fe3d3bd
diff --git a/lib/libc/putchar.c b/lib/libc/putchar.c
index 3472b24..340bdd8 100644
--- a/lib/libc/putchar.c
+++ b/lib/libc/putchar.c
@@ -1,14 +1,13 @@
 /*
- * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2023, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
 #include <stdio.h>
 
-int __putchar(int c)
+#pragma weak putchar
+int putchar(int c)
 {
 	return c;
 }
-
-int putchar(int c) __attribute__((weak,alias("__putchar")));