[libc] puts implementation for baremetal (#98051)

This is a simple baremetal implementation of puts akin to putchar.

Author: petrhosek

libc/config/baremetal/arm/entrypoints.txt

@@ -85,6 +85,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     # stdio.h entrypoints
     libc.src.stdio.printf
     libc.src.stdio.putchar
+    libc.src.stdio.puts
     libc.src.stdio.remove
     libc.src.stdio.snprintf
     libc.src.stdio.sprintf

libc/config/baremetal/riscv/entrypoints.txt

@@ -81,6 +81,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     # stdio.h entrypoints
     libc.src.stdio.printf
     libc.src.stdio.putchar
+    libc.src.stdio.puts
     libc.src.stdio.remove
     libc.src.stdio.snprintf
     libc.src.stdio.sprintf

libc/src/stdio/baremetal/CMakeLists.txt

@@ -32,6 +32,17 @@ add_entrypoint_object(
     libc.src.__support.CPP.string_view
 )
 
+add_entrypoint_object(
+  puts
+  SRCS
+    puts.cpp
+  HDRS
+    ../puts.h
+  DEPENDS
+    libc.src.__support.OSUtil.osutil
+    libc.src.__support.CPP.string_view
+)
+
 add_entrypoint_object(
   vprintf
   SRCS

libc/src/stdio/baremetal/puts.cpp

@@ -0,0 +1,25 @@
+//===-- Implementation of puts for baremetal-------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdio/puts.h"
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/OSUtil/io.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(int, puts, (const char *__restrict str)) {
+  cpp::string_view str_view(str);
+
+  // TODO: Can we combine these to avoid needing two writes?
+  write_to_stderr(str_view);
+  write_to_stderr("\n");
+
+  return 0;
+}
+
+} // namespace LIBC_NAMESPACE