internal/pkg: increase output buffer size

This avoids truncating unreasonably long lines from llvm.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/exec.go

@@ -259,6 +259,10 @@ func scanVerbose(
 ) {
 	defer close(done)
 	s := bufio.NewScanner(r)
+	s.Buffer(
+		make([]byte, bufio.MaxScanTokenSize),
+		bufio.MaxScanTokenSize<<12,
+	)
 	for s.Scan() {
 		msg.Verbose(prefix, s.Text())
 	}