cc: change cas to newcase

Change the name of cas() in cc to newcase() to avoid a NIX conflict.
cas() is used in cc to create a new Case struct. There is a name
conflict in that cas() is a commonly-used
name for compare and swap. Since cas() is only used internally
in the compiler in 3 places, change the name to avoid a wider
conflict with the NIX runtime. This issue might well come up on
other OSes in the future anyway, as the name is fairly common.

R=rsc
CC=golang-dev
https://golang.org/cl/5294071

src/cmd/5c/gc.h

@@ -304,7 +304,7 @@ void	gpseudo(int, Sym*, Node*);
 int	swcmp(const void*, const void*);
 void	doswit(Node*);
 void	swit1(C1*, int, int32, Node*);
-void	cas(void);
+void	newcase(void);
 void	bitload(Node*, Node*, Node*, Node*, Node*);
 void	bitstore(Node*, Node*, Node*, Node*, Node*);
 int	mulcon(Node*, Node*);

src/cmd/6c/gc.h

@@ -299,7 +299,7 @@ void	gpseudo(int, Sym*, Node*);
 int	swcmp(const void*, const void*);
 void	doswit(Node*);
 void	swit1(C1*, int, int32, Node*);
-void	cas(void);
+void	newcase(void);
 void	bitload(Node*, Node*, Node*, Node*, Node*);
 void	bitstore(Node*, Node*, Node*, Node*, Node*);
 int32	outstring(char*, int32);

src/cmd/8c/gc.h

@@ -304,7 +304,7 @@ void	gpseudo(int, Sym*, Node*);
 int	swcmp(const void*, const void*);
 void	doswit(Node*);
 void	swit1(C1*, int, int32, Node*);
-void	cas(void);
+void	newcase(void);
 void	bitload(Node*, Node*, Node*, Node*, Node*);
 void	bitstore(Node*, Node*, Node*, Node*, Node*);
 int32	outstring(char*, int32);

src/cmd/cc/pgen.c

@@ -266,7 +266,7 @@ loop:
 		if(cases == C)
 			diag(n, "case/default outside a switch");
 		if(l == Z) {
-			cas();
+			newcase();
 			cases->val = 0;
 			cases->def = 1;
 			cases->label = pc;
@@ -278,7 +278,7 @@ loop:
 			goto rloop;
 		if(l->op == OCONST)
 		if(typeword[l->type->etype] && l->type->etype != TIND) {
-			cas();
+			newcase();
 			cases->val = l->vconst;
 			cases->def = 0;
 			cases->label = pc;
@@ -303,7 +303,7 @@ loop:
 
 		cn = cases;
 		cases = C;
-		cas();
+		newcase();
 
 		sbc = breakpc;
 		breakpc = pc;

src/cmd/cc/pswt.c

@@ -92,7 +92,7 @@ doswit(Node *n)
 }
 
 void
-cas(void)
+newcase(void)
 {
 	Case *c;