Fix iostream related issues (#5047)

* add stubs for more exception throw calls

Fixes https://github.com/esp8266/Arduino/issues/3358

* libc: make putc_r implementation weak

newlib provides its own implementation of _putc_r, which will call
_write_r (possibly after buffering). Make our implementation weak to
allow using the one from newlib.

Fixes https://github.com/esp8266/Arduino/issues/4630

* libc: fix incorrect return value of _write_r call

Should return number of bytes written, actually returned zero. This
resulted in std::cout going into failed state after the first write.

* tests: add test for output to std::cout

cores/esp8266/abi.cpp

@@ -127,7 +127,24 @@ void __throw_out_of_range(const char* str)
     (void) str;
     panic();
 }
+
+void __throw_bad_cast(void)
+{
+    panic();
 }
 
+void __throw_ios_failure(const char* str)
+{
+    (void) str;
+    panic();
+}
+
+void __throw_runtime_error(const char* str)
+{
+    (void) str;
+    panic();
+}
+} // namespace std
+
 // TODO: rebuild windows toolchain to make this unnecessary:
 void* __dso_handle;