Fix incorrect temporary insertion in loop conditions with statements (#4873)

When the condition of an AstWhile loop contains a statement (e.g.
through an AstExprStmt), temporaries inserted in that statement need to
go before that statement, not in the AstWhile precondition.

src/V3Premit.cpp

@@ -176,8 +176,10 @@ class PremitVisitor final : public VNVisitor {
     if (stmtp->user1SetOnce()) return; \
     VL_RESTORER(m_assignLhs); \
     VL_RESTORER(m_stmtp); \
+    VL_RESTORER(m_inWhileCondp); \
     m_assignLhs = false; \
-    m_stmtp = stmtp
+    m_stmtp = stmtp; \
+    m_inWhileCondp = nullptr
 
     void visit(AstWhile* nodep) override {
         UINFO(4, "  WHILE  " << nodep << endl);