cpu/esp32: fix of ctor and newlib initialization

Module `newlib` is now used by default. Therefore, the separation of initialization of ctors and the newlibc is not needed any longer. Instead of calling `do_global_ctors` and `_init` separately, `__libc_init_array` is called. Explicit function `do_global_ctors` is removed.

cpu/esp32/startup.c

@@ -93,7 +93,6 @@ extern void bootloader_clock_configure(void);
 
 /* forward declarations */
 static void system_init(void);
-static void do_global_ctors(void);
 static void intr_matrix_clear(void);
 
 typedef int32_t esp_err_t;
@@ -279,22 +278,19 @@ static NORETURN void IRAM system_init (void)
     /* Disable the hold flag of all RTC GPIO pins */
     RTCCNTL.hold_force.val = 0;
 
-    /* execute constructors */
-    do_global_ctors();
+    /*
+     * initialization of newlib, includes the ctors initialization and
+     * and the execution of stdio_init in _init of newlib_syscalls_default
+     */
+    extern void __libc_init_array(void);
+    __libc_init_array();
 
     /* init watchdogs */
     system_wdt_init();
 
     /* init random number generator */
     srand(hwrand());
 
-    /*
-     * initialization as it should be called from newlibc (includes the
-     * execution of stdio_init)
-    */
-    extern void _init(void);
-    _init();
-
     /* add SPI RAM to heap if enabled */
     #if CONFIG_SPIRAM_SUPPORT && CONFIG_SPIRAM_BOOT_INIT
     spi_ram_heap_init();
@@ -345,18 +341,6 @@ static NORETURN void IRAM system_init (void)
     UNREACHABLE();
 }
 
-static void do_global_ctors(void)
-{
-    #if 0 /* TODO when real ctors are used exist */
-    extern uint32_t* __init_array_start;
-    extern uint32_t* __init_array_end;
-    for (uint32_t* up = __init_array_end - 1; up >= __init_array_start; --up) {
-        void (*fp)(void) = (void (*)(void))up;
-        fp();
-    }
-    #endif
-}
-
 static void intr_matrix_clear(void)
 {
     /* attach all peripheral interrupt sources (Technical Reference, Table 7) */