ci/diag.sh: Try to make sed unbuffered

Author: tavianator

.github/diag.sh

@@ -8,8 +8,13 @@
 
 set -eu
 
+SEDFLAGS="-En"
+if sed -u 's/s/s/' </dev/null &>/dev/null; then
+    SEDFLAGS="${SEDFLAGS}u"
+fi
+
 filter() {
-    sed -En 'p; s/^([^:]*):([^:]*):([^:]*): (warning|error): (.*)$/::\4 file=\1,line=\2,col=\3,title=Compiler \4::\5/p'
+    sed $SEDFLAGS 'p; s/^([^:]*):([^:]*):([^:]*): (warning|error): (.*)$/::\4 file=\1,line=\2,col=\3,title=Compiler \4::\5/p'
 }
 
 exec "$@" > >(filter) 2> >(filter >&2)