Output a helpful msg about configure only if the command fails.

Makefile.in

@@ -133,11 +133,10 @@ rounding.h: rounding.c rsync.h proto.h
 	@rm -f rounding.out
 
 simd-checksum-x86_64.o: simd-checksum-x86_64.cpp
-	@echo "If this fails to compile and you can't fix it, re-run $(srcdir)/configure with --disable-simd."
-	$(CXX) -I. $(CXXFLAGS) $(CPPFLAGS) -c -o $@ $(srcdir)/simd-checksum-x86_64.cpp
+	@$(srcdir)/cmdormsg disable-simd $(CXX) -I. $(CXXFLAGS) $(CPPFLAGS) -c -o $@ $(srcdir)/simd-checksum-x86_64.cpp
 
 lib/md5-asm-x86_64.o: lib/md5-asm-x86_64.S config.h lib/md-defines.h
-	$(CC) -I. @NOEXECSTACK@ -c -o $@ $(srcdir)/lib/md5-asm-x86_64.S
+	@$(srcdir)/cmdormsg disable-asm $(CC) -I. @NOEXECSTACK@ -c -o $@ $(srcdir)/lib/md5-asm-x86_64.S
 
 tls$(EXEEXT): $(TLS_OBJ)
 	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(TLS_OBJ) $(LIBS)

cmdormsg

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+srcdir=`dirname $0`
+opt="$1"
+shift
+
+echo "$*"
+if ! "${@}"; then
+    echo "If you can't fix the issue, re-run $srcdir/configure with --$opt."
+    exit 1
+fi