[clang] [clang][AVR] Restrict range of assembly constraint 'G' (PR #76561)

[Lu Weining via cfe-commits]

SixWeining wrote:

LGTM. I have checked with https://gcc.gnu.org/onlinedocs/gccint/Machine-Constraints.html. 'G' stands for "A floating point constant 0.0". But I'd like to wait others' opinion.

https://github.com/llvm/llvm-project/pull/76561