[libc] Change default behaviour of baremetal/printf to use stdout (#143703)

In #94078, `write_to_stdout` had not been fully implemented. However,
now that it has been implemented, to conform with the C standard
(7.23.6.3. The printf function, specifically point 2), we use `stdout`.
This issue is tracked in #94685.

- Also prefer `static constexpr`
- Made it explicit that we are writing to `stdout`

Author: saturn691

libc/src/stdio/baremetal/printf.cpp

@@ -21,8 +21,8 @@ namespace LIBC_NAMESPACE_DECL {
 
 namespace {
 
-LIBC_INLINE int raw_write_hook(cpp::string_view new_str, void *) {
-  write_to_stderr(new_str);
+LIBC_INLINE int stdout_write_hook(cpp::string_view new_str, void *) {
+  write_to_stdout(new_str);
   return printf_core::WRITE_OK;
 }
 
@@ -35,11 +35,11 @@ LLVM_LIBC_FUNCTION(int, printf, (const char *__restrict format, ...)) {
                                  // and pointer semantics, as well as handling
                                  // destruction automatically.
   va_end(vlist);
-  constexpr size_t BUFF_SIZE = 1024;
+  static constexpr size_t BUFF_SIZE = 1024;
   char buffer[BUFF_SIZE];
 
   printf_core::WriteBuffer<printf_core::WriteMode::FLUSH_TO_STREAM> wb(
-      buffer, BUFF_SIZE, &raw_write_hook, nullptr);
+      buffer, BUFF_SIZE, &stdout_write_hook, nullptr);
   printf_core::Writer<printf_core::WriteMode::FLUSH_TO_STREAM> writer(wb);
 
   int retval = printf_core::printf_main(&writer, format, args);

libc/src/stdio/baremetal/putchar.cpp

@@ -16,7 +16,7 @@ namespace LIBC_NAMESPACE_DECL {
 LLVM_LIBC_FUNCTION(int, putchar, (int c)) {
   char uc = static_cast<char>(c);
 
-  write_to_stderr(cpp::string_view(&uc, 1));
+  write_to_stdout(cpp::string_view(&uc, 1));
 
   return 0;
 }

libc/src/stdio/baremetal/puts.cpp

@@ -17,8 +17,8 @@ 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");
+  write_to_stdout(str_view);
+  write_to_stdout("\n");
 
   return 0;
 }

libc/src/stdio/baremetal/vprintf.cpp

@@ -21,8 +21,8 @@ namespace LIBC_NAMESPACE_DECL {
 
 namespace {
 
-LIBC_INLINE int raw_write_hook(cpp::string_view new_str, void *) {
-  write_to_stderr(new_str);
+LIBC_INLINE int stdout_write_hook(cpp::string_view new_str, void *) {
+  write_to_stdout(new_str);
   return printf_core::WRITE_OK;
 }
 
@@ -33,11 +33,11 @@ LLVM_LIBC_FUNCTION(int, vprintf,
   internal::ArgList args(vlist); // This holder class allows for easier copying
                                  // and pointer semantics, as well as handling
                                  // destruction automatically.
-  constexpr size_t BUFF_SIZE = 1024;
+  static constexpr size_t BUFF_SIZE = 1024;
   char buffer[BUFF_SIZE];
 
   printf_core::WriteBuffer<printf_core::WriteMode::FLUSH_TO_STREAM> wb(
-      buffer, BUFF_SIZE, &raw_write_hook, nullptr);
+      buffer, BUFF_SIZE, &stdout_write_hook, nullptr);
   printf_core::Writer<printf_core::WriteMode::FLUSH_TO_STREAM> writer(wb);
 
   int retval = printf_core::printf_main(&writer, format, args);