[Bug target/107731] loongarch Operand Modifiers are not documented

[chenglulu at loongson dot cn via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107731

--- Comment #7 from chenglulu <chenglulu at loongson dot cn> ---
(In reply to Andrew Pinski from comment #3)
> MIPS nor RISCV does not define a %c either.

These two architectures can also fail under the following conditions:

void
test(void)
{
  asm (".long %c0"
       ::"i"(0x12345678));
}