Add AVR to LLVM_ALL_TARGETS

[xiangzhai]

Summary

Hi LLVM developers,

As George mentioned in D32991 :

I tried to run llvm-mc to check which relocations are produced here but got an error: /home/umb/LLVM/llvm-build/bin/llvm-mc: : error: unable to get target for 'avr-unknown-linux', see --version and --triple.

As Rafael suggested: AVR is not in LLVM_ALL_TARGETS. I wonder if we should change it before D32991.

Please review my patch, thanks a lot!

Regards,
Leslie Zhai

[dylanmckay]

I personally wouldn't be comfortable making the backend a non-experimental backend just yet.

There are still a lot of bugs which forbid most complex programs from being compiled. Once it is somewhat more usable, I'd definitely push for making the backend a first-class citizen.

On top of this, when we actually promote the backend to a default target, we would need to remove AVR FROM the LLVM_EXPERIMENTAL_TARGETS_TO_BUILD option

CMakeLists.txt

 set(LLVM_CMAKE_PATH ${LLVM_MAIN_SRC_DIR}/cmake/modules)
 set(LLVM_EXAMPLES_BINARY_DIR ${LLVM_BINARY_DIR}/examples)
 set(LLVM_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/include)
 
 set(LLVM_ALL_TARGETS
   AArch64
   AMDGPU
   ARM
+  AVR
   BPF
   Hexagon
   Lanai
   Mips
   MSP430
   NVPTX
   PowerPC
   RISCV