According to https://www.nongnu.org/avr-libc/user-manual/inline_asm.html, 'G' only represents floating point constant '0.0'. And avr-gcc also rejects other non-zero FP values.
Fixes https://github.com/llvm/llvm-project/issues/60204 Reviewed By: jacquesguan Differential Revision: https://reviews.llvm.org/D145659
Reviewed By: MaskRay Differential Revision: https://reviews.llvm.org/D120468