Add android toolchain to GN build system

[randyrossi]

Problem

Android toolchain needed for GN build

Summary of Changes

Adding an android toolchain for arm and x86_64 target
cpus. Subsequent CLs may add target arch to select
armv6, armv7, arm64 and x86 targets if required.

Added a check to only attempt to run tests when
current_os == host_os, otherwise cross compiled tests
attempt to execute on the wrong architecture and fail.

Need to temporarily omit lib/messages from android build
due to RNG dependency on openssl.

fixes #2242

[github-actions]

Size increase report for "gn_nrf-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

[github-actions]

Size increase report for "gn_linux-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

[github-actions]

Size increase report for "nrf-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-nrf52840-lock-example.out and ./pull_artifact/chip-nrf52840-lock-example.out:

sections,vmsize,filesize

[github-actions]

Size increase report for "nrfconnect-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-nrf52840-lock-example.elf and ./pull_artifact/chip-nrf52840-lock-example.elf:

sections,vmsize,filesize

[github-actions]

Size increase report for "linux-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-standalone-demo.out and ./pull_artifact/chip-standalone-demo.out:

sections,vmsize,filesize

[github-actions]

Size increase report for "esp32-example-build"

File	Section	File	VM

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-wifi-echo.elf and ./pull_artifact/chip-wifi-echo.elf:

sections,vmsize,filesize