libgo: don't use \? in grep pattern

It's not supported by Solaris grep.  Just use * instead; it matches
    more but it shouldn't matter.
    
    Fixes https://gcc.gnu.org/PR91764
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/195238

From-SVN: r275700

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-ceb1e4f5614b4772eed44f9cf57780e52f44753e
+5af62eda697da21155091cf5375ed9edb4639b67
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/match.sh

@@ -135,7 +135,7 @@ for f in $gofiles; do
 
     if test x$tag1 != xnonmatchingtag -a x$tag2 != xnonmatchingtag; then
 	# Pipe through cat so that `set -e` doesn't affect fgrep.
-	tags=`sed '/^package /q' < $f | grep '^// \?+build ' | cat`
+	tags=`sed '/^package /q' < $f | grep '^// *+build ' | cat`
 	omatch=true
 	first=true
 	match=false

libgo/testsuite/gotest

@@ -326,7 +326,7 @@ x)
 	    esac
 
 	    if test x$tag1 != xnonmatchingtag -a x$tag2 != xnonmatchingtag; then
-		tags=`sed '/^package /q' < $f | grep '^// \?+build '`
+		tags=`sed '/^package /q' < $f | grep '^// *+build '`
 		omatch=true
 		first=true
 		match=false