printf and puts used ets_printf before. Unfortunately, ets_printf adds an additional \r for each \n which is not consistent with other RIOT platforms. As a result some automatic tests failed. Therefore, both functions write now character-wise directly to the UART interface.
If module esp_idf_heap is used, the memory management functions _malloc_r, _realloc_r, _calloc_r and _free_r have to be overridden by wrapper functions to use the heap_* functions of module _esp_idf_heap. However, this can lead to multiple symbol errors for these functions for some applications. To solve this symbol conflict, _malloc_r, _realloc_r, _calloc_r and _free_r functions are renamed to __wrap_* and the linker options are extended by -Wl,-wrap option when module esp_idf_heap is used.
When standard C libraries are added to BASELIBS to group them together with all other modules, there are multiple definitions for the putchar function. The one that is defined writing to the UART as standard output and the one that is provided by the standard C libraries. To solve this symbol conflict, putchar and getchar functions that use the UART as standard output/input are renamed to __wrap_putchar and __wrap_getchar and the linker options are extended by -Wl,-wrap option.
Adds a memset function `system_secure_memset` which cannot be optimized out by the compiler. It uses the libsodium approach of weak symbols. Function system_secure_memset calls the standard memset. Calling an empty function declared with weak attribute after the memset call, prevents the compiler to optimize it out. The overhead is only one function call.
Xtensa newlib version requires pthread_setcancelstate as symbol. Therefore, the module pthread was always used, which in turn requires the module xtimer. The xtimer module, however, uses TIMER_DEV(0). Therefore, tests/timers failed for TIMER_DEV(0).
