[MCAsmParser] .irpc: correctly handle quoted string

The quotes should be stripped.

Improve the test to check all of Identifier, Integer, and String.

GNU assembler also supports `.irpc c,"" a` but there is no real world
use case. So don't implement it.

Author: MaskRay

llvm/lib/MC/MCParser/AsmParser.cpp

@@ -5780,7 +5780,8 @@ bool AsmParser::parseDirectiveIrpc(SMLoc DirectiveLoc) {
   SmallString<256> Buf;
   raw_svector_ostream OS(Buf);
 
-  StringRef Values = A.front().front().getString();
+  StringRef Values = A[0][0].is(AsmToken::String) ? A[0][0].getStringContents()
+                                                  : A[0][0].getString();
   for (std::size_t I = 0, End = Values.size(); I != End; ++I) {
     MCAsmMacroArgument Arg;
     Arg.emplace_back(AsmToken::Identifier, Values.slice(I, I + 1));

llvm/test/MC/AsmParser/macro-irpc.s

@@ -1,12 +1,20 @@
 // RUN: llvm-mc -triple x86_64-unknown-unknown %s | FileCheck %s
 
-.irpc foo,123
+.irpc foo,"123"
         .long \foo
 .endr
+.irpc foo,ab
+        .long 0x\foo
+.endr
+.irpc foo,""
+.endr
 
 // CHECK: long 1
 // CHECK: long 2
 // CHECK: long 3
+// CHECK: long 10
+// CHECK: long 11
+// CHECK-NOT: long
 
 .irpc foo,123
 .irpc bar,45