all: add target-features string to all targets

This makes sure that the LLVM target features match the one generated by
Clang:

  - This fixes a bug introduced when setting the target CPU for all
    targets: Cortex-M4 would now start using floating point operations
    while they were disabled in C.
  - This will make it possible in the future to inline C functions in Go
    and vice versa. This will need some more work though.

There is a code size impact. Cortex-M4 targets are increased slightly in
binary size while Cortex-M0 targets tend to be reduced a little bit.
Other than that, there is little impact.

targets/nintendoswitch.json

@@ -1,6 +1,7 @@
 {
   "llvm-target": "aarch64",
   "cpu": "cortex-a57",
+  "features": "+aes,+crc,+crypto,+fp-armv8,+neon,+sha2",
   "build-tags": ["nintendoswitch", "arm64"],
   "scheduler": "tasks",
   "goos": "linux",