Remove needless toolchain files and variable settings.

Unnecessary to set CMAKE_SYSTEM_NAME and CMAKE_SYSTEM_PROCESSOR, these values
are set by default. It also allows to use any C99-compliant compiler by using
the default CC enviroment variable or by setting the CMAKE_C_COMPILER value
using the build script's --cmake-param argument.

JerryScript-DCO-1.0-Signed-off-by: Robert Sipka [email protected]

Author: robertsipka