Move .C to .CPP in the code (#5696)

Use g++ to compile core files to get additional C++ checks on the code.

Also move libb64 constants to PROGMEM, saving ~128 bytes of heap when used.

cores/esp8266/libc_replacements.cpp

@@ -0,0 +1,134 @@
+/*
+ libc_replacements.c - replaces libc functions with functions
+ from Espressif SDK
+
+ Copyright (c) 2015 Ivan Grokhotkov. All rights reserved.
+ This file is part of the esp8266 core for Arduino environment.
+
+ This library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ This library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with this library; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+ Modified 03 April 2015 by Markus Sattler
+
+ */
+
+#include <stddef.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include <limits.h>
+#include <errno.h>
+#include <string.h>
+#include <time.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/reent.h>
+
+#include "ets_sys.h"
+#include "os_type.h"
+#include "osapi.h"
+#include "mem.h"
+#include "user_interface.h"
+#include "debug.h"
+
+extern "C" {
+
+int ICACHE_RAM_ATTR _open_r (struct _reent* unused, const char *ptr, int mode) {
+    (void)unused;
+    (void)ptr;
+    (void)mode;
+    return 0;
+}
+
+int ICACHE_RAM_ATTR _close_r(struct _reent* unused, int file) {
+    (void)unused;
+    (void)file;
+    return 0;
+}
+
+int ICACHE_RAM_ATTR _fstat_r(struct _reent* unused, int file, struct stat *st) {
+    (void)unused;
+    (void)file;
+    st->st_mode = S_IFCHR;
+    return 0;
+}
+
+int ICACHE_RAM_ATTR _lseek_r(struct _reent* unused, int file, int ptr, int dir) {
+    (void)unused;
+    (void)file;
+    (void)ptr;
+    (void)dir;
+    return 0;
+}
+
+int ICACHE_RAM_ATTR _read_r(struct _reent* unused, int file, char *ptr, int len) {
+    (void)unused;
+    (void)file;
+    (void)ptr;
+    (void)len;
+    return 0;
+}
+
+int ICACHE_RAM_ATTR _write_r(struct _reent* r, int file, char *ptr, int len) {
+    (void) r;
+    int pos = len;
+    if (file == STDOUT_FILENO) {
+        while(pos--) {
+            ets_putc(*ptr);
+            ++ptr;
+        }
+    }
+    return len;
+}
+
+int ICACHE_RAM_ATTR _putc_r(struct _reent* r, int c, FILE* file) __attribute__((weak));
+
+int ICACHE_RAM_ATTR _putc_r(struct _reent* r, int c, FILE* file) {
+    (void) r;
+    if (file->_file == STDOUT_FILENO) {
+        return ets_putc(c);
+    }
+    return EOF;
+}
+
+int ICACHE_RAM_ATTR puts(const char * str) {
+    char c;
+    while((c = *str) != 0) {
+        ets_putc(c);
+        ++str;
+    }
+    ets_putc('\n');
+    return true;
+}
+
+#undef putchar
+int ICACHE_RAM_ATTR putchar(int c) {
+    ets_putc(c);
+    return c;
+}
+
+void _exit(int status) {
+    (void) status;
+    abort();
+}
+
+int atexit(void (*func)()) {
+    (void) func;
+    return 0;
+}
+
+};