snc: fixed recognition of line markers for windows CPP output

This fixes error and warnign messages on windows so they refer
to the original source file. Also refactored line marker regexes
and allow whitespace before and after the '#'.

src/snc/snl.re

@@ -153,6 +153,11 @@ static char *strdupft(uchar *start, uchar *stop) {
 	return result;
 }
 
+/*
+ * Note: Linemarkers differ between compilers. The MS C preprocessor outputs
+ * "#line <linenum> <filename>" directives, while gcc leaves off the "line".
+ */
+
 /*!re2c
 	NL	= [\n];
 	ANY	= [^];
@@ -165,6 +170,7 @@ static char *strdupft(uchar *start, uchar *stop) {
 	FS	= [fFlL];
 	IS	= [uUlL]*;
 	ESC	= [\\] ([abfnrtv?'"\\] | "x" HEX+ | OCT+);
+	LINE	= SPC* "#" (SPC* "line")? SPC+;
 */
 
 static int scan(Scanner *s, Token *t) {
@@ -193,15 +199,15 @@ snl:
 				s->line++;
 				goto snl;
 			}
+	LINE		{
+				line_marker_part = cursor - s->tok;
+				goto line_marker;
+			}
 	["]		{
 				s->tok = s->end = cursor;
 				goto string_const;
 			}
 	"/*"		{ goto comment; }
-	"#" SPC*	{
-				line_marker_part = cursor - s->tok;
-				goto line_marker;
-			}
 	"%{"		{
 				s->tok = cursor;
 				in_c_code = 1;
@@ -410,7 +416,7 @@ c_code:
 				LITERAL(CCODE, embedded_c_code, strdupft(s->tok, cursor - 2));
 			}
 	.		{ goto c_code; }
-	"#" SPC+	{
+	LINE		{
 				line_marker_part = cursor - s->tok;
 				goto line_marker;
 			}