Always turn on the -+ flag in cpp

C99 comments have been the default in compilers for something like 20 years
now. This means we don't need to remember to turn it on when porting software,
and gets rid of cryptic errors about unterminated character constants when
someone writes something like:

	// Didn't need to...

We still accept the flag to avoid breaking mkfiles, but we do nothing with it.

This also removes the documentation, since the option does nothing now.

sys/man/1/cpp

@@ -67,9 +67,6 @@ Do not insert
 .RB `` #line ''
 directives into the output.
 .TP
-.B -+
-Understand C++ comments.
-.TP
 .B -.
 Inhibit include search in the source's directory.
 .TP

sys/man/1/pcc

@@ -25,11 +25,6 @@ The object files are then loaded using one of the loaders described in
 .IR 2l (1).
 The options are:
 .TP \w'\fL-D\ \fIname=def\ 'u
-.B "-+
-Accept C++
-.B //
-comments.
-.TP
 .BI -o " out"
 Place loader output in file
 .I out

sys/src/cmd/cpp/cpp.c

@@ -28,7 +28,6 @@ main(int argc, char **argv)
 	maketokenrow(3, &tr);
 	expandlex();
 	setup(argc, argv);
-	fixlex();
 	iniths();
 	genline();
 	process(&tr);

sys/src/cmd/cpp/cpp.h

@@ -86,7 +86,6 @@ extern	unsigned long namebit[077+1];
 enum errtype { WARNING, ERROR, FATAL };
 
 void	expandlex(void);
-void	fixlex(void);
 void	setup(int, char **);
 #define gettokens cpp_gettokens
 int	gettokens(Tokenrow *, int);

sys/src/cmd/cpp/lex.c

@@ -285,14 +285,6 @@ expandlex(void)
 	}
 }
 
-void
-fixlex(void)
-{
-	/* do C++ comments? */
-	if (Cplusplus==0)
-		bigfsm['/'][COM1] = bigfsm['x'][COM1];
-}
-
 /*
  * fill in a row of tokens from input, terminated by NL or END
  * First token is put at trp->lp.

sys/src/cmd/cpp/nlist.c

@@ -8,7 +8,6 @@ extern	char	*optarg;
 extern	int	optind;
 int	verbose;
 int	Mflag;
-int	Cplusplus;
 int	nolineinfo;
 Nlist	*kwdefined;
 char	wd[128];
@@ -142,7 +141,7 @@ setup(int argc, char **argv)
 			verbose++;
 			break;
 		case '+':
-			Cplusplus++;
+			/* Ignored for compatibility */
 			break;
 		case 'i':
 			debuginclude++;

sys/src/cmd/pcc.c

@@ -65,7 +65,7 @@ main(int argc, char *argv[])
 	while(argc > 0) {
 		ARGBEGIN {
 		case '+':
-			append(&cpp, smprint("-%c", ARGC()));
+			/* No-op for compatibility */
 			break;
 		case 'c':
 			cflag = 1;