LoongArch: Avoid non-returning indirect jumps through $ra [PR110136]

LoongArch: Avoid non-returning indirect jumps through $ra [PR110136]

Micro-architecture unconditionally treats a "jr $ra" as "return from subroutine",
hence doing "jr $ra" would interfere with both subroutine return prediction and
the more general indirect branch prediction.

Therefore, a problem like PR110136 can cause a significant increase in branch error
prediction rate and affect performance. The same problem exists with "indirect_jump".

gcc/ChangeLog:

	PR target/110136
	* config/loongarch/loongarch.md: Modify the register constraints for template
	"jumptable" and "indirect_jump" from "r" to "e".

Co-authored-by: Andrew Pinski <apinski@marvell.com>