Use MAKEFLAGS to pass args to make in all.sh
Use MAKEFLAGS to pass args to make in all.sh

Modify the script at tests/scripts/all.sh to export the variable
MAKEFLAGS with -j if it was not set before. This should decrease the
total runtime of tests/scripts/all.sh by letting make run multiple jobs
in parallel. Also, add a check at the top of the script to cause a
failure if the environment is not Linux.

NXPmicro/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls