sys/uart_stdio: compile with -Wno-cast-function-type

tests: add more hardware in the loop tests

native: define PROVIDES_PM_SET_LOWEST

pkg/libcose: Use RIOT random_bytes instead of randombytes

pkg/hacl: Use RIOT random_bytes instead of randombytes

pkg/tweetnacl: Use RIOT random_bytes instead of randombytes

core: make assert() an expression.

 tests/unittests: add empty list clist_foreach case 

examples/filesystem: fix typos and cleanup

Add clist_foreach empty list test case which should:

* not call `func`
* return `NULL`

core/clist: make clist_foreach() return break-causing node

The "verbose" alternative for assert() is now an expression and
can be used in all the places that a funcion call can be used.

tools/check: use RIOTTOOLS variable

boards/nucleo-l496zg: add initial support

cpu/cc2538: remove obsolete periph file guard

boards/common/atmega: gracefully handle CKDIV8 fuse

Follow up to #9067 and part of #8821

gnrc/netif/hdr.h: Optimized structure layout

Reordered struct members to not waste memory due to padding.

Before:
``` C
typedef struct {
    uint8_t src_l2addr_len;
    uint8_t dst_l2addr_len;
    kernel_pid_t if_pid;    // <-- 16 bit, is aligned to 16 bit
    uint8_t flags;
    uint8_t __padding_byte; // <-- Inserted to fulfill padding requirements
    int16_t rssi;           // <-- 16 bit, is NOT aligned to 16 bit
    uint8_t lqi;
    uint8_t __padding_byte2;// <-- Inserted to fulfill padding requirements
} gnrc_netif_hdr_t;
```

Now:
``` C
typedef struct {
    uint8_t src_l2addr_len;
    uint8_t dst_l2addr_len;
    kernel_pid_t if_pid;    // <-- 16 bit, is aligned to 16 bit
    uint8_t flags;
    uint8_t lqi;
    int16_t rssi;           // <-- 16 bit, is aligned to 16 bit
} gnrc_netif_hdr_t;
```

When build for the `bluepill` board, the new layout reduces the size by 2 bytes.

makefiles/info.inc.mk: add a info-debug-variable-% target

tests: unittests: disable for new efm32 boards.

cpu/cortexm: explicitly set -march=armv6s-m for crotexm0(plus)

drivers/io1_xplained: improve driver and add support for the sdcard and light sensor

drivers: add driver for FXOS8700 3-axis accelerometer/magnetometer

enc28j60: fix compilation with l2 stats enabled

 cpu/nrf5x: define nrfmin feature in nrf5x_common