[dev.cc] cmd/6a, etc: fix line number accounting during #ifdef

Lines beginning with #ifdef, #else, #endif were not incrementing
the line number, resulting in bad line number information for
assembly files with #ifdefs.

Example:

	#ifndef GOARCH_ppc64
	#endif
	#ifdef GOARCH_ppc64le
	#endif

	TEXT ·use(SB),7,$0
		RET

Before this change, the line number recorded for use in 6a -S output
(and in the runtime information in the binary) was 4 too low.

Change-Id: I23e599112ec9919f72e53ac82d9bebbbae3439ed
Reviewed-on: https://go-review.googlesource.com/3783Reviewed-by: Rob Pike <r@golang.org>

src/cmd/cc/lexbody

@@ -572,6 +572,8 @@ getc(void)
 	c = peekc;
 	if(c != IGN) {
 		peekc = IGN;
+		if(c == '\n')
+			lineno++;
 		return c;
 	}
 	c = GETC();
@@ -633,7 +635,7 @@ loop:
 				return l;
 			}
 		}
-		peekc = c;
+		unget(c);
 		return l;
 	}
 	switch(c)

src/cmd/internal/asm/lexbody.go

@@ -534,6 +534,9 @@ func getc() int {
 	c = peekc
 	if c != IGN {
 		peekc = IGN
+		if c == '\n' {
+			Lineno++
+		}
 		return c
 	}
 
@@ -599,6 +602,7 @@ loop:
 		}
 
 		peekc = c
+		unget(c)
 		return l
 	}