[RISCV] Fix parseBareSymbol to not double-parse top-level operators

By failing to lex the token we end up both parsing it as a binary
operator ourselves and parsing it as a unary operator when calling
parseExpression on the RHS. For plus this is harmless but for minus this
parses "foo - 4" as "foo - -4", effectively treating a top-level minus
as a plus.

Fixes #54105

Reviewed By: asb, MaskRay

Differential Revision: https://reviews.llvm.org/D120635

(cherry picked from commit 6aa8521)

Author: jrtc27

llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

@@ -1607,9 +1607,11 @@ OperandMatchResultTy RISCVAsmParser::parseBareSymbol(OperandVector &Operands) {
     return MatchOperand_Success;
   case AsmToken::Plus:
     Opcode = MCBinaryExpr::Add;
+    getLexer().Lex();
     break;
   case AsmToken::Minus:
     Opcode = MCBinaryExpr::Sub;
+    getLexer().Lex();
     break;
   }
 

llvm/test/MC/RISCV/rvi-pseudos.s

@@ -187,3 +187,9 @@ sw a3, zero, a4
 # CHECK: auipc a5, %pcrel_hi((255+a_symbol)-4)
 # CHECK: addi  a5, a5, %pcrel_lo(.Lpcrel_hi30)
 lla a5, (0xFF + a_symbol) - 4
+
+## Check that we don't double-parse a top-level minus.
+# CHECK: .Lpcrel_hi31:
+# CHECK: auipc a5, %pcrel_hi(a_symbol-4)
+# CHECK: addi  a5, a5, %pcrel_lo(.Lpcrel_hi31)
+lla a5, a_symbol - 4