Use g++ as LD (mpm is buggered anyway).

src/cmd/mpm/mkfile

diff --git a/src/cmd/mpm/mkfile b/src/cmd/mpm/mkfile
index c6bae4b..5c9df7d 100644
--- a/src/cmd/mpm/mkfile
+++ b/src/cmd/mpm/mkfile
@@ -9,6 +9,8 @@
 
 HFILES=misc.h\
 
+LD=g++
+
 <$PLAN9/src/mkone
 CFLAGS=