The generated arm_neon.h header isn't -Wdeclaration-after-statement
compliant when targeting -mbig-endian. Update the generator to declare
the return value, if any, first before any other arguments that might
need to be "reversed" from little endian to big.
Another approach would have been to try to ignore this warning in system
headers, though that might not be precise for tokens involved in macro
expansion. See also: https://reviews.llvm.org/D116833#3236209.
Link: https://github.com/ClangBuiltLinux/linux/issues/1603
Fixes: https://github.com/llvm/llvm-project/issues/54062
Does armebv7 work when you only have aarch64?
It probably does just by virtue of aarch64 not knowing what v7 is and defaulting to v8 but double check what happens there.
If the emitter is used for both arm and aarch64 then testing one would be acceptable. Since you can't really do an if has arm do this else in a lit test like this.