[lld][ELF] Support relocations R_AVR_LO8_LDI_GS/R_AVR_HI8_LDI_GS

[benshi001]

ping ...

R_AVR_LO8_LDI_GS is all the same with R_AVR_LO8_LDI_PM, except restricted in range [0, 0x1ffff].
R_AVR_HI8_LDI_GS is all the same with R_AVR_HI8_LDI_PM, except restricted in range [0, 0x1ffff].

lld/ELF/Arch/AVR.cpp

RelExpr AVR::getRelExpr(RelType type, const Symbol &s,
   case R_AVR_LO8_LDI:
   case R_AVR_LO8_LDI_NEG:
   case R_AVR_HI8_LDI:
   case R_AVR_HI8_LDI_NEG:
   case R_AVR_HH8_LDI_NEG:
   case R_AVR_HH8_LDI:
   case R_AVR_MS8_LDI_NEG:
   case R_AVR_MS8_LDI:
+  case R_AVR_LO8_LDI_GS:
   case R_AVR_LO8_LDI_PM:
   case R_AVR_LO8_LDI_PM_NEG:
+  case R_AVR_HI8_LDI_GS:
   case R_AVR_HI8_LDI_PM:
   case R_AVR_HI8_LDI_PM_NEG:
   case R_AVR_HH8_LDI_PM:
   case R_AVR_HH8_LDI_PM_NEG:
   case R_AVR_LDS_STS_16:
   case R_AVR_PORT5:
   case R_AVR_PORT6:
   case R_AVR_CALL:
case R_AVR_HH8_LDI:
     break;
   case R_AVR_MS8_LDI_NEG:
     writeLDI(loc, (-val >> 24) & 0xff);
     break;
   case R_AVR_MS8_LDI:
     writeLDI(loc, (val >> 24) & 0xff);
     break;
 
+  case R_AVR_LO8_LDI_GS:
+    checkUInt(loc, val, 17, rel);
+    [[fallthrough]];
   case R_AVR_LO8_LDI_PM:
     checkAlignment(loc, val, 2, rel);
     writeLDI(loc, (val >> 1) & 0xff);
     break;
+  case R_AVR_HI8_LDI_GS:
+    checkUInt(loc, val, 17, rel);
+    [[fallthrough]];
   case R_AVR_HI8_LDI_PM:
     checkAlignment(loc, val, 2, rel);
     writeLDI(loc, (val >> 9) & 0xff);
     break;
   case R_AVR_HH8_LDI_PM:
     checkAlignment(loc, val, 2, rel);
     writeLDI(loc, (val >> 17) & 0xff);
     break;

lld/test/ELF/avr-reloc.s

 ; REQUIRES: avr
 ; RUN: llvm-mc -filetype=obj -triple=avr -mcpu=atmega328p %s -o %t0.o
-; RUN: ld.lld %t0.o --defsym=a=0x12345678 --defsym=b=30 -o %t0
+; RUN: ld.lld %t0.o --defsym=a=0x12345678 --defsym=b=30 --defsym=c=0x15554 -o %t0
 ; RUN: llvm-objdump -d --print-imm-hex --mcpu=atmega328p %t0 | \
 ; RUN:     FileCheck --check-prefixes=CHECK,AVR %s
 ; RUN: llvm-objdump -s --mcpu=atmega328p %t0 | \
 ; RUN:     FileCheck --check-prefixes=HEX,AVRHEX %s
 ; RUN: llvm-mc -filetype=obj -triple=avr -mcpu=attiny10 %s --defsym=TINY=1 -o %t1.o
-; RUN: ld.lld %t1.o --defsym=a=0x12345678 --defsym=b=30 -o %t1
+; RUN: ld.lld %t1.o --defsym=a=0x12345678 --defsym=b=30 --defsym=c=0x15554 -o %t1
 ; RUN: llvm-objdump -d --print-imm-hex --mcpu=attiny10 %t1 | FileCheck %s
 ; RUN: llvm-objdump -s --mcpu=attiny10 %t1 | \
 ; RUN:     FileCheck --check-prefixes=HEX,TINYHEX %s
 
 .section .LDI,"ax",@progbits
 ; CHECK-LABEL: section .LDI:
 ; CHECK:       ldi     r20, 0x78
 ; CHECK-NEXT:  ldi     r20, 0x56
 ; CHECK-NEXT:  ldi     r20, 0x34
 ; CHECK-NEXT:  ldi     r20, 0x12
 ; CHECK-NEXT:  ldi     r20, 0x3c
 ; CHECK-NEXT:  ldi     r20, 0x2b
 ; CHECK-NEXT:  ldi     r20, 0x1a
+; CHECK-NEXT:  ldi     r20, 0xaa
+; CHECK-NEXT:  ldi     r20, 0xaa
 ; CHECK-NEXT:  ldi     r20, 0xff
+
 ldi r20, lo8(a)     ; R_AVR_LO8_LDI
 ldi r20, hi8(a)     ; R_AVR_HI8_LDI
 ldi r20, hh8(a)     ; R_AVR_HH8_LDI
 ldi r20, hhi8(a)    ; R_AVR_MS8_LDI
 
 ldi r20, pm_lo8(a)  ; R_AVR_LO8_LDI_PM
 ldi r20, pm_hi8(a)  ; R_AVR_HI8_LDI_PM
 ldi r20, pm_hh8(a)  ; R_AVR_HH8_LDI_PM
 
+ldi r20, lo8_gs(c)  ; R_AVR_LO8_LDI_GS
+ldi r20, hi8_gs(c)  ; R_AVR_HI8_LDI_GS
+
 ldi r20, b+225
 
 .section .LDI_NEG,"ax",@progbits
 ; CHECK-LABEL: section .LDI_NEG:
 ; CHECK:       ldi     r20, 0x88
 ; CHECK-NEXT:  ldi     r20, 0xa9
 ; CHECK-NEXT:  ldi     r20, 0xcb
 ; CHECK-NEXT:  ldi     r20, 0xed