MIPS: Register .set created symbols

When the `.set` directive is used to equate a symbol (`.set symbol,
expression`), ensure the created symbol is registered in the symbol
table.

Author: MaskRay

llvm/lib/Target/Mips/AsmParser/MipsAsmParser.cpp

@@ -7507,7 +7507,7 @@ bool MipsAsmParser::parseSetAssignment() {
   if (MCParserUtils::parseAssignmentExpression(Name, /* allow_redef */ true,
                                                Parser, Sym, Value))
     return true;
-  Sym->setVariableValue(Value);
+  getStreamer().emitAssignment(Sym, Value);
 
   return false;
 }

llvm/test/MC/Mips/set-defined-symbol.s

@@ -16,3 +16,7 @@ b:
 # CHECK-NOT: b:
 # CHECK-NOT: foo:
 # CHECK: <bar>:
+
+# CHECK: <dot>:
+.set dot, .
+  nop

llvm/test/MC/Mips/set-sym-recursive.s

@@ -1,9 +1,11 @@
 # RUN: not llvm-mc -filetype=obj -triple=mips64 %s -o /dev/null 2>&1 | FileCheck %s --implicit-check-not=error:
 
-.set B, B + 1
-
 # CHECK: :[[@LINE+1]]:11: error: cyclic dependency detected for symbol 'A'
 .set A, A + 1
 # CHECK: :[[@LINE+1]]:7: error: expected relocatable expression
 .word A
 .word A
+
+# CHECK: :[[@LINE+2]]:11: error: cyclic dependency detected for symbol 'B'
+# CHECK: :[[@LINE+1]]:11: error: expression could not be evaluated
+.set B, B + 1