cmd/cc: allow to call nested packages from within C code

E.g. sync/atomic.LoadInt32() can be called as sync»atomic·LoadInt32()

R=rsc
CC=golang-dev
https://golang.org/cl/6448057

src/cmd/cc/lex.c

@@ -377,11 +377,16 @@ lookup(void)
 		symb[1] = '"';
 	}
 
-	// turn · into .
 	for(r=w=symb; *r; r++) {
+		// turn · (U+00B7) into .
+		// turn ∕ (U+2215) into /
 		if((uchar)*r == 0xc2 && (uchar)*(r+1) == 0xb7) {
 			*w++ = '.';
 			r++;
+		}else if((uchar)*r == 0xe2 && (uchar)*(r+1) == 0x88 && (uchar)*(r+2) == 0x95) {
+			*w++ = '/';
+			r++;
+			r++;
 		}else
 			*w++ = *r;
 	}

src/cmd/cc/lexbody

@@ -251,11 +251,16 @@ lookup(void)
 		symb[1] = '"';
 	}
 
-	// turn · into .
 	for(r=w=symb; *r; r++) {
+		// turn · (U+00B7) into .
+		// turn ∕ (U+2215) into /
 		if((uchar)*r == 0xc2 && (uchar)*(r+1) == 0xb7) {
 			*w++ = '.';
 			r++;
+		}else if((uchar)*r == 0xe2 && (uchar)*(r+1) == 0x88 && (uchar)*(r+2) == 0x95) {
+			*w++ = '/';
+			r++;
+			r++;
 		}else
 			*w++ = *r;
 	}