feat: rename weak in features.h to __weak

The internal `features.h` defines macro `weak`, and it prevents us porting
third-party code including the identifier.

crt/crt1.c

@@ -6,8 +6,8 @@
 #include "crt_arch.h"
 
 int main();
-weak void _init();
-weak void _fini();
+__weak void _init();
+__weak void _fini();
 int __libc_start_main(int (*)(), int, char **,
 	void (*)(), void(*)(), void(*)());
 

crt/rcrt1.c

@@ -3,8 +3,8 @@
 #include "../ldso/dlstart.c"
 
 int main();
-weak void _init();
-weak void _fini();
+__weak void _init();
+__weak void _fini();
 int __libc_start_main(int (*)(), int, char **,
 	void (*)(), void(*)(), void(*)());
 

ldso/dynlink.c

@@ -159,7 +159,7 @@ static struct fdpic_dummy_loadmap app_dummy_loadmap;
 
 struct debug *_dl_debug_addr = &debug;
 
-extern weak hidden char __ehdr_start[];
+extern __weak hidden char __ehdr_start[];
 
 extern hidden int __malloc_replaced;
 

src/env/__init_tls.c

@@ -77,7 +77,7 @@ typedef Elf32_Phdr Phdr;
 typedef Elf64_Phdr Phdr;
 #endif
 
-extern weak hidden const size_t _DYNAMIC[];
+extern __weak hidden const size_t _DYNAMIC[];
 
 static void static_init_tls(size_t *aux)
 {

src/env/__libc_start_main.c

@@ -10,7 +10,7 @@
 static void dummy(void) {}
 weak_alias(dummy, _init);
 
-extern weak hidden void (*const __init_array_start)(void), (*const __init_array_end)(void);
+extern __weak hidden void (*const __init_array_start)(void), (*const __init_array_end)(void);
 
 static void dummy1(void *p) {}
 weak_alias(dummy1, __init_ssp);

src/exit/exit.c

@@ -15,7 +15,7 @@ weak_alias(dummy, __funcs_on_exit);
 weak_alias(dummy, __stdio_exit);
 weak_alias(dummy, _fini);
 
-extern weak hidden void (*const __fini_array_start)(void), (*const __fini_array_end)(void);
+extern __weak hidden void (*const __fini_array_start)(void), (*const __fini_array_end)(void);
 
 static void libc_exit_fini(void)
 {

src/include/features.h

@@ -3,7 +3,7 @@
 
 #include "../../include/features.h"
 
-#define weak __attribute__((__weak__))
+#define __weak __attribute__((__weak__))
 #define hidden __attribute__((__visibility__("hidden")))
 #define weak_alias(old, new) \
 	extern __typeof(old) new __attribute__((__weak__, __alias__(#old)))

src/ldso/dl_iterate_phdr.c

@@ -5,7 +5,7 @@
 
 #define AUX_CNT 38
 
-extern weak hidden const size_t _DYNAMIC[];
+extern __weak hidden const size_t _DYNAMIC[];
 
 static int static_dl_iterate_phdr(int(*callback)(struct dl_phdr_info *info, size_t size, void *data), void *data)
 {