x11/kitty: fix build on riscv64 and runtime on powerpc64

Disable LTO.
On riscv64:
Hard-float 'd' ABI can't be used for a target that doesn't support the D instruction set extension (ignoring target-abi)
ld: error: lto.tmp: cannot link object files with different floating-point ABI
cc: error: linker command failed with exit code 1 (use -v to see invocation)

On powerpc64, LTO is broken with LLVM.