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cc2: Fix parameters order after popctx() fix

The commit f124441b fixed a memory corruption problem but it also
introduced an important regression because the order of parameters
was reversed.

--- a/src/cmd/cc/cc2/cc2.h

+++ b/src/cmd/cc/cc2/cc2.h

@@ -168,7 +168,7 @@

 		Node *stmt;

 		Inst *inst;

 	} u;

-	Symbol *next;

+	Symbol *next, *prev;

 	Symbol *h_next;

 };

--- a/src/cmd/cc/cc2/symbol.c

+++ b/src/cmd/cc/cc2/symbol.c

@@ -10,6 +10,7 @@

 #define NR_SYMHASH  64

 Symbol *locals;

+static Symbol *tail;

 static Symbol *symtab[NR_SYMHASH];

 static int infunction;

@@ -31,11 +32,11 @@

 void

 popctx(void)

 {

-	Symbol *sym, *next;

+	Symbol *sym, *prev;

 	infunction = 0;

-	for (sym = locals; sym; sym = next) {

-		next = sym->next;

+	for (sym = tail; sym; sym = prev) {

+		prev = sym->prev;

 		/*

 		 * Symbols are inserted in the hash in the inverted

 		 * order they are found in locals and it is impossible

@@ -51,7 +52,7 @@

 			symtab[sym->id & NR_SYMHASH-1] = sym->h_next;

 		freesym(sym);

 	}

-	locals = NULL;

+	locals = tail = NULL;

 }

 Symbol *

@@ -74,8 +75,13 @@

 	sym = xcalloc(1, sizeof(*sym));

 	sym->id = id;

 	if (infunction) {

-		sym->next = locals;

-		locals = sym;

+		sym->next = NULL;

+		sym->prev = tail;

+		if (tail)

+			tail->next = sym;

+		tail = sym;

+		if (!locals)

+			locals = sym;

 	}

 	if (id != TMPSYM) {

 		sym->h_next = *htab;