Do not pass CFLAGS to gcc while building native tool

Do not pass CFLAGS/LDFLAGS to gcc while building native tool, The 
needed flags has been passed by xxx_CFLAGS=$(CFLAGS_FOR_BUILD).
---
 tools/locktest/Makefile.am |    2 ++
 tools/rpcdebug/Makefile.am |    2 ++
 tools/rpcgen/Makefile.am   |    2 ++
 3 files changed, 6 insertions(+), 0 deletions(-)

Index: nfs-utils-1.2.8/tools/locktest/Makefile.am
===================================================================
--- nfs-utils-1.2.8.orig/tools/locktest/Makefile.am
+++ nfs-utils-1.2.8/tools/locktest/Makefile.am
@@ -1,6 +1,8 @@
 ## Process this file with automake to produce Makefile.in
 
 CC=$(CC_FOR_BUILD)
+CFLAGS=
+LDFLAGS=
 LIBTOOL = @LIBTOOL@ --tag=CC
 
 noinst_PROGRAMS = testlk
Index: nfs-utils-1.2.8/tools/rpcgen/Makefile.am
===================================================================
--- nfs-utils-1.2.8.orig/tools/rpcgen/Makefile.am
+++ nfs-utils-1.2.8/tools/rpcgen/Makefile.am
@@ -1,6 +1,8 @@
 ## Process this file with automake to produce Makefile.in
 
 CC=$(CC_FOR_BUILD)
+CFLAGS=
+LDFLAGS=
 LIBTOOL = @LIBTOOL@ --tag=CC
 
 noinst_PROGRAMS = rpcgen