[ELF][Hexagon] Improve error message for unknown relocations

[MaskRay]

Summary

Like rLLD354040

Previously, for unrecognized relocation types, in -no-pie/-pie mode, we got something like:

foo.o: unrecognized relocation ...

In -shared mode:

error: can't create dynamic relocation ... against symbol: yyy in readonly segment

Delete the default case from Hexagon::getRelExpr and add the error there. We will get consistent error message like error: unknown relocation (1024) against symbol foo

[ruiu]

LGTM but please wait for Sid.

ELF/Arch/Hexagon.cpp

for (size_t bit = 0; bit != 32; ++bit) {
     }
   }
   return result;
 }
 
 RelExpr Hexagon::getRelExpr(RelType type, const Symbol &s,
                             const uint8_t *loc) const {
   switch (type) {
+  case R_HEX_NONE:
+    return R_NONE;
+  case R_HEX_6_X:
+  case R_HEX_8_X:
+  case R_HEX_9_X:
+  case R_HEX_10_X:
+  case R_HEX_11_X:
+  case R_HEX_12_X:
+  case R_HEX_16_X:
+  case R_HEX_32:
+  case R_HEX_32_6_X:
+  case R_HEX_HI16:
+  case R_HEX_LO16:
+    return R_ABS;
   case R_HEX_B9_PCREL:
   case R_HEX_B9_PCREL_X:
   case R_HEX_B13_PCREL:
   case R_HEX_B15_PCREL:
   case R_HEX_B15_PCREL_X:
   case R_HEX_6_PCREL_X:
   case R_HEX_32_PCREL:
     return R_PC;
   case R_HEX_B22_PCREL:
   case R_HEX_PLT_B22_PCREL:
   case R_HEX_B22_PCREL_X:
   case R_HEX_B32_PCREL_X:
     return R_PLT_PC;
   case R_HEX_GOT_11_X:
   case R_HEX_GOT_16_X:
   case R_HEX_GOT_32_6_X:
     return R_HEXAGON_GOT;
   default:
-    return R_ABS;
+    error(getErrorLocation(loc) + "unknown relocation (" + Twine(type) +
+          ") against symbol " + toString(s));
+    return R_NONE;
   }
 }
 
 static uint32_t findMaskR6(uint32_t insn) {
   // There are (arguably too) many relocation masks for the DSP's
   // R_HEX_6_X type.  The table below is used to select the correct mask
   // for the given instruction.
   struct InstructionMask {
case R_HEX_B32_PCREL_X:
     break;
   case R_HEX_HI16:
     or32le(loc, applyMask(0x00c03fff, val >> 16));
     break;
   case R_HEX_LO16:
     or32le(loc, applyMask(0x00c03fff, val));
     break;
   default:
-    error(getErrorLocation(loc) + "unrecognized relocation " + toString(type));
-    break;
+    llvm_unreachable("unknown relocation");
   }
 }
 
 void Hexagon::writePltHeader(uint8_t *buf) const {
   const uint8_t pltData[] = {
       0x00, 0x40, 0x00, 0x00, // { immext (#0)
       0x1c, 0xc0, 0x49, 0x6a, //   r28 = add (pc, ##GOT0@PCREL) } # @GOT0
       0x0e, 0x42, 0x9c, 0xe2, // { r14 -= add (r28, #16)  # offset of GOTn