nfs-utils: build tools with target compiler

nfs-utils: build tools with target compiler

Some tools were built with CC_FOR_BUILD which points to the target
compiler. The current patch avoided issues by deleting some of the
binaries during install.

This patch replaces the CC_FOR_BUILD with CC so the tools are built with
the target compiler. This means the binaries no longer need to be
deleted.

I stumbled upon this by trying to globally add "--ffile-prefix-map", which
is not supported by my host GCC, to get rid of some "buildpaths" QA Warnings.

Cc: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Pascal Bach <pascal.bach@siemens.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>