tools/nolibc: add prototypes for non-static functions

With -Wmissing-prototypes the compiler will warn about non-static
functions which don't have a prototype defined.
This warning doesn't make much sense for nolibc itself but for user code
it is still useful.
To pacify the compiler add prototypes next to the function definitions,
similar to how it is handled elsewhere in the kernel.

Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20250123-nolibc-prototype-v1-1-e1afc5c1999a@weissschuh.net
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

Author: t-8ch

tools/include/nolibc/arch-mips.h

@@ -179,6 +179,7 @@
 })
 
 /* startup code, note that it's called __start on MIPS */
+void __start(void);
 void __attribute__((weak, noreturn)) __nolibc_entrypoint __no_stack_protector __start(void)
 {
 	__asm__ volatile (

tools/include/nolibc/crt.h

@@ -10,6 +10,7 @@
 char **environ __attribute__((weak));
 const unsigned long *_auxv __attribute__((weak));
 
+void _start(void);
 static void __stack_chk_init(void);
 static void exit(int);
 
@@ -22,6 +23,7 @@ extern void (*const __init_array_end[])(int, char **, char**) __attribute__((wea
 extern void (*const __fini_array_start[])(void) __attribute__((weak));
 extern void (*const __fini_array_end[])(void) __attribute__((weak));
 
+void _start_c(long *sp);
 __attribute__((weak,used))
 void _start_c(long *sp)
 {

tools/include/nolibc/signal.h

@@ -13,6 +13,7 @@
 #include "sys.h"
 
 /* This one is not marked static as it's needed by libgcc for divide by zero */
+int raise(int signal);
 __attribute__((weak,unused,section(".text.nolibc_raise")))
 int raise(int signal)
 {

tools/include/nolibc/stackprotector.h

@@ -18,6 +18,7 @@
  * triggering stack protector errors themselves
  */
 
+void __stack_chk_fail(void);
 __attribute__((weak,used,noreturn,section(".text.nolibc_stack_chk")))
 void __stack_chk_fail(void)
 {
@@ -28,6 +29,7 @@ void __stack_chk_fail(void)
 	for (;;);
 }
 
+void __stack_chk_fail_local(void);
 __attribute__((weak,noreturn,section(".text.nolibc_stack_chk")))
 void __stack_chk_fail_local(void)
 {

tools/include/nolibc/stdlib.h

@@ -30,6 +30,7 @@ static __attribute__((unused)) char itoa_buffer[21];
  */
 
 /* must be exported, as it's used by libgcc for various divide functions */
+void abort(void);
 __attribute__((weak,unused,noreturn,section(".text.nolibc_abort")))
 void abort(void)
 {

tools/include/nolibc/string.h

@@ -32,6 +32,7 @@ int memcmp(const void *s1, const void *s2, size_t n)
 /* might be ignored by the compiler without -ffreestanding, then found as
  * missing.
  */
+void *memmove(void *dst, const void *src, size_t len);
 __attribute__((weak,unused,section(".text.nolibc_memmove")))
 void *memmove(void *dst, const void *src, size_t len)
 {
@@ -56,6 +57,7 @@ void *memmove(void *dst, const void *src, size_t len)
 
 #ifndef NOLIBC_ARCH_HAS_MEMCPY
 /* must be exported, as it's used by libgcc on ARM */
+void *memcpy(void *dst, const void *src, size_t len);
 __attribute__((weak,unused,section(".text.nolibc_memcpy")))
 void *memcpy(void *dst, const void *src, size_t len)
 {
@@ -73,6 +75,7 @@ void *memcpy(void *dst, const void *src, size_t len)
 /* might be ignored by the compiler without -ffreestanding, then found as
  * missing.
  */
+void *memset(void *dst, int b, size_t len);
 __attribute__((weak,unused,section(".text.nolibc_memset")))
 void *memset(void *dst, int b, size_t len)
 {
@@ -124,6 +127,7 @@ char *strcpy(char *dst, const char *src)
  * thus itself, hence the asm() statement below that's meant to disable this
  * confusing practice.
  */
+size_t strlen(const char *str);
 __attribute__((weak,unused,section(".text.nolibc_strlen")))
 size_t strlen(const char *str)
 {