blinky app won't build unless upgrading to newer arm-toolchain

Following instructions [here](http://mynewt.apache.org/latest/get_started/native_install/cross_tools.html#installing-the-arm-toolchain-for-mac-os-x) if I install the 4.9 arm toolchain, and build the app, I get following error message:

$ newt create-image nrf52_blinky 1.0.0
Compiling repos/apache-mynewt-core/hw/drivers/uart/src/uart.c
Assembling repos/apache-mynewt-core/hw/bsp/nordic_pca10040/src/arch/cortex_m4/gcc_startup_nrf52.s
Assembling repos/apache-mynewt-core/hw/bsp/nordic_pca10040/src/arch/cortex_m4/gcc_startup_nrf52_split.s
Compiling repos/apache-mynewt-core/hw/bsp/nordic_pca10040/src/sbrk.c
Compiling repos/apache-mynewt-core/hw/hal/src/hal_common.c
. . .
. . .
Compiling repos/apache-mynewt-core/libc/baselibc/src/memfile.c
Compiling repos/apache-mynewt-core/libc/baselibc/src/memmem.c
Error: repos/apache-mynewt-core/kernel/os/src/os_mempool.c: In function 'os_memblock_from':
**repos/apache-mynewt-core/kernel/os/src/os_mempool.c:308:5: error: implicit declaration of function 'static_assert' [-Werror=implicit-function-declaration]
static_assert(sizeof block_addr == sizeof baddr32,
^
cc1: all warnings being treated as errors**

After advancing the toolchain to "version 8.2.1 20181213", the above mentioned problem was resolved. So, I think the document should be updated to avoid this issue.

Open the linked “Installing the ARM Toolchain for Mac OS X” documentation section and compare its required version with the reported 4.9 failure and 8.2.1 resolution. Update the documented recommendation so the blinky app build instructions use a working toolchain version; done when the page no longer directs users to the failing version.

Written by the indexing model from the issue text.