gotest: multiple +build lines must all be true

The code that handled +build lines did not correctly require them to all
    be true.  While looking into this I discovered that multiple +build
    lines were mishandled in a different way, because the shell does not
    preseve line breaks in backquoted data.  Look for the +build token to
    tell us when we are switching from one +build line to another.
    
    Reviewed-on: https://go-review.googlesource.com/25460

From-SVN: r239100

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-0fb416a7bed076bdfef168480789bb2994a58de3
+3096ac81185edacbf800783f0f803d1c419dccdd
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/testsuite/gotest

@@ -313,13 +313,9 @@ x)
 	    esac
 
 	    if test x$tag1 != xnonmatchingtag -a x$tag2 != xnonmatchingtag; then
-		taglines=`sed '/^package /q' < $f | fgrep '// +build '`
-		if test "$taglines" = ""; then
+		tags=`sed '/^package /q' < $f | fgrep '// +build '`
 		omatch=true
-		else
-		    omatch=false
-		fi
-		for tags in $taglines; do
+		first=true
 		match=false
 		for tag in $tags; do
 		    reverse=false
@@ -331,7 +327,15 @@ x)
 		    esac
 
 		    case $tag in
-			"//" | "+build")
+		    "//")
+			;;
+		    "+build")
+			if test "$first" = "true"; then
+			    first=false
+			elif test "$match" = "false"; then
+			    omatch=false
+			fi
+			match=false
 			;;
 		    $goos | $goarch | cgo)
 			match=true
@@ -358,10 +362,10 @@ x)
 			fi
 		    fi
 		done
-		    if test "$match" = "true"; then
-			omatch=true
+
+		if test "$match" = "false" -a "$first" = "false"; then
+		    omatch=false
 		fi
-		done
 
 		if test "$omatch" = "true"; then
 		    gofiles="$gofiles $f"