CMakeSystem: include toolchain file after setting CMAKE_HOST_ (#13796)

Make the CMAKE_HOST_* variables always available in the toolchain file.
They are when the file is included in CMakeDetermineSystem.cmake, and
now also here.  For the non-cross-compiling case this does not change
anything at all.

Alex
Merge topic 'CrossCompilingFix13796' into next

efb19b6 CMakeSystem: include toolchain file after setting CMAKE_HOST_ (#13796)
Add support files for C, C++ and ASM for the IAR toolchain.

The original feature request is at http://www.cmake.org/Bug/view.php?id=10176
Documentation can be found at http://www.iar.com/website1/1.0.1.0/675/1/

Alex
Add regexps for the IAR toolchain to the vendor list.

The IAR compilers produce object files where the plain strings at least
sometimes can't be found, see:

  http://www.cmake.org/Bug/view.php?id=10176#c19598

Alex
Add IAR to the CMakeDetectC(XX)CompilerID.c(pp).in

With the AVR IAR compiler this can't be found, but it works e.g. for the
ARM AVR compiler.

Alex
Merge topic 'AddIARToolchain2' into next

d118b8b Add IAR to the CMakeDetectC(XX)CompilerID.c(pp).in
d33f406 Add regexps for the IAR toolchain to the vendor list.
22fb73a Add support files for C, C++ and ASM for the IAR toolchain.