[RISCV] Mark symbols used in inline asm for relocations as referenced (llvm#104925)

Commit 5cd8d53 taught RISCVMergeBaseOffset to handle inline asm,
however
there is at least one case uncovered for integrated as.

In the example below compiler generates pcrel relocation
(mcmodel=medany)
```
    volatile double double_val = 1.0;
    void foo() {
        asm volatile("fld f0, %0 \n\t" : : "m"(double_val) : "memory");
    }
```

And fails with the folliwng error
```
    error: could not find corresponding %pcrel_hi
          |       "fld f0, %0 \n\t"
    <inline asm>:1:2: note: instantiated into assembly here
          |         fld f0, %pcrel_lo(.Lpcrel_hi0)(a0)
```

After transformations MachineFunction contains inline asm instructions
with
'.Lpcrel_hi0' symbol that is not defined in inline asm, but referenced.
```
   ... = AUIPC ...(riscv-pcrel-hi) @double_val, pre-instr-symbol <mcsymbol .Lpcrel_hi0>
   INLINEASM &"fld f0, $0 \0A\09" ... target-flags(riscv-pcrel-lo) <mcsymbol .Lpcrel_hi0>
```

So, when AsmParser processes 'fld', it has to create a new symbol as
'.Lpcrel_hi0' already exists but not known to be referenced in inline
asm.
AsmParser avoids conflicts by renaming referenced by 'fld' symbol with
'.Lpcrel_hi00' name which does not exist. Resulting erroneous asm
```
    .Lpcrel_hi0:
        auipc   a0, %pcrel_hi(double_val)
        #APP
        fld     ft0, %pcrel_lo(.Lpcrel_hi00)(a0)
```

This change adds symbols used in memory operands to the list of
referenced ones.

Godbolt link: https://godbolt.org/z/aqrrsWKoK -- on the left you can
find incorrect labels for the integrated-as and on the right an error
when compiling to the binary object.

Author: asi-sc

llvm/lib/Target/RISCV/RISCVAsmPrinter.cpp

@@ -396,6 +396,15 @@ bool RISCVAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
     OS << MCO.getImm();
   else if (Offset.isGlobal() || Offset.isBlockAddress() || Offset.isMCSymbol())
     OS << *MCO.getExpr();
+
+  if (Offset.isMCSymbol())
+    MMI->getContext().registerInlineAsmLabel(Offset.getMCSymbol());
+  if (Offset.isBlockAddress()) {
+    const BlockAddress *BA = Offset.getBlockAddress();
+    MCSymbol *Sym = GetBlockAddressSymbol(BA);
+    MMI->getContext().registerInlineAsmLabel(Sym);
+  }
+
   OS << "(" << RISCVInstPrinter::getRegisterName(AddrReg.getReg()) << ")";
   return false;
 }